Acceleration (change in velocity during time t) is proportional to the net force\ acting on the body
but inversely proportional to the mass (inertia)
1) Introduction
video to understand Newton's 3 laws of motion
here is another one:
Newton invented Calculus to explain motions.
His most famous equation is referred as Newton’s second law.
1) Could you find this equation knowing:
- Force (symbol F) causes the velocity to change from an initial value (Vi) to a final value (Vf) . As the force increases, the change in velocity increases.
(∆V = Vfinal - Vinitial =change in velocity )
-The mass or inertia (m) opposes the change in velocity. As m increases, the change in velocity decreases.
- Increasing the time (∆t) during which the force is applied increases the change in velocity.
Call the change in velocity ∆V . (∆V = Vfinal -Vinitial)
Write: ∆V = _________________ Use F, m and ∆t
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2) The second law is now best known as:
The total force (net force) acting on a body is equal to the mass times its acceleration
Or F = _________
a is the _____________ , m is the _____________, F is the ______________
a and F are vector quantities. They have magnitude and direction.
But we will only work in 1D in 10th grade. We will only consider 2 directions:
right and left or up and down. A negative sign shows the down or left direction.
For example: g = -9.8 m/s2 means the acceleration due to gravity is pointing down.
Newton's formula tells us that 1N is the force necessary to accelerate a 1-kg mass at the rate of 1 m/s2
1N is about the force required to lift an apple
Units for F is newton (of kg m/s/s), units for a is m/s2 , units for mass is kg.
F ∆T = m ∆V
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3) Here is another way to understand F = m a . remember that g is the acceleration due to gravity. (acceleration of a free-falling object).
g is 32feet/s/s or 22 mph/s or 10m/s/s. weight is mass x g . Sometime, we express the acceleration in gs.
F = m a can be written as F = (mg) ( a/g). or force = weigth x (acceleration in gs).
That means if you apply 1 pound of force on 1 pound object, the acceleration will be 1 g or 22mph/s .
150 pounds of force on 150 weight, acceleration = 1 g. That's why all objects fall at the same rate if we can neglect friction.
Say you are in your car , at rest, and in 1 second you reach about 20mph. You force you feel on your back is equal to your weight.
If you reach 40mph in 1 second, you feel 2g or twice your weight. You can compute the acceleration astronauts have to undergo
during take off is compute in gs, about 3gs. so they feel 3 times their weight that includes their outfit.
4) DEMONTRATIONS / experiments of thought.
Funny movie to watch: professor Julius Sumner or you can skip it and do the experiments below.
A) Attach 2 toy cars by a spring. put 1kg in one. stretch the spring. mark the middle. the spring exert the same force on both cars.
Let go the cars. Do they get in the middle at the same time? Which one is faster ? Which one has the smaller inertia ?
(that is which one resists change in motion the least?
So more mass = less acceleration.
So the car with the least mass m will go faster and will reach the middle first. Same force but not the same acceleration.
Mathematically: M a = F = m a
B) Use a round spring scale. attach a mass of 1kg. Read the weight in Newton. weight = mg = ______ N. This is the gravitational force (pull) exerted by the Earth on the mass. This pull stretches the spring and moves the arrow.
You can call it the rest weight. Now quickly move the spring scale upward such as the spring scale is accelerated upward along the vertical.
Call the acceleration of the spring a. While you accelerate the scale read the it. new weight = __________ N
Do you read the same weight ? less ? more ? explain
Because of inertia the mass wants to stay at rest and resists motion. The spring stretches more and the scale reads more.
The pull on the spring is more than the rest weight mg. The pull is : new weight = mg + ma = weight at rest + ma .
with a the acceleration of the spring. Next time you take an elevator, take a bathroom scale with you.
As the elevator moves up (accelerates up), you weight increases by ma. You feel heavier because the bottom of the elevator pushes you, while you want to stay at rest. The force acts on the elevator, not on you. (this phenomenon stops if the elevator moves at a constant speed. When if a frame of reference
that moves at a constant speed, you can't tell if you moving or no. So no weird effect like a change in your rest weight)
MORE ADVANCED:
If the elevator accelerates, the weight shown by the scale increases.
In the frame of reference if the elevator, the person is at rest.
THe person feels a force (called pseudo force) pulling him/her down.
This is the same kind of force you feel in a train when it suddenly stops. (or speeds up)
The magnitude of this force is ma . m is the mass of the person and a the acceleration of the elevator.
In the frame of reference of the elevator you have : -ma - mg + T = 0 (T is the support force of the scale
pushing back on you). So T = mg + ma. The scale " feels " the same force T and reads its magnitude.
C) same experience but accelerate the spring downward. Is the reading the same? less ? more ? new weight = __________N
Now the spring is less stretched, the reading is less than the rest weight. new pull = new weight = mg - ma.
If you take an elevator to go down, as the elevator accelerates downward, you feel lighter. You push less on the scale/ (or bottom of elevator)..
(MORE ADVANCED : In the frame of reference of the elevator, you feel a force pulling you up . the magnitude is ma.
In this frame of reference, you are at rest such as : - mg + T + ma = 0 or T = mg - ma . T is the reading on the scale)
D) If you drop the spring scale. The scale is in free fall. What is the reading ?
the spring is not stretch anymore, the mass and the spring are falling at the same rate, the mass is weightless.
a = g so pull = new weight = mg - ma = 0
If you could jump from the table with a bathroom scale attached to your feet, same thing. you would be weightless.
you are both falling at the same rate, you are not pushing on the scale.
Astronauts in space are weightless. (when they orbit the EArth). 2 forces act on them. The force of gravity and the centrifugal force
(the same force you experience in a spinning ride) . The 2 forces balance each other in the the frame of reference of the spaceship orbiting the EArth.`.
so the astronauts feel weightless. Because, they don't need to work against gravity, they experience a loss in muscle.
IN SHORT :
source picture:
From Paul Hewitt book, Conceptual Physics.
The picture shows that if you are in free-fall, the scale does not read anything.
Not because you have no weight but because the scale is falling with you, so you
are not pushing on it anymore. You are : weightless . You are falling with the scale.
astronauts experiencing free-fall. They are said to be " weightless "
The force of gravity is still acting on them but because they fall inside a plane
nothing (like the ground ) is pushing back on them. They don' t feel their weight.
In the international station you are also weightless because you are constantly falling toward the Earth.
The station never reaches the EArth because it also has a tangential motion.
HERe is an expected consequence of zero gravity
E) Here in an experiment to understand better the weightless phenomenon. Get a Styrofoam cup and make holes at the bottom.
Fill it with water. Of course the water will leak because of the pull of gravity. But now drop the cup full of water. (above a sink).
the cup and the water are in free-fall and the water does not leak !
F) get 2 spheres of different mass. In free-fall, they both the ground at the same time. They have the same acceleration because:
small mass: F1 = m a1 (newtons 2nd law) and F1 = m g (force = pull due to gravity) so a1 = m g / m = g
large mass: F2 = m a2 and F2 = Mg so g2 = Mg / M = g
Do the experiment with a feather and a penny in a vacuum.
G) Imagine 2 little girls. they both weighs 70 pounds. one is standing up a hill and the other one at the bottom, ready to read a spring scale/
The top girl jumps on the spring scale. The reading is less than 70 ? more ? 70 pounds ?
The scale is pushing back on you, the reaction is your " new weight ".
There is a way to estimate how much push you get.(your new weight) Your energy on the hill = weight x height. (called potential energy).
(energy is force applied x distance it is applied, here the force is the pull due to gravity, the distance is the height).
In a first approximation, we can say your energy is conserved (neglecting loss of energy to heat and noise) .
so real weight x height = force on spring scale x distance the spring is compressed. Say you jump 1 meter (about 1 yard)
and the spring moves by about 10cm (stiff spring) then you weigth will be multiplied by 10. If you jump of the floor, it hurts more
because the floor hardly moves (by a few micro meters) so you will feel a greater force. It is a force multiplier.
H) 2 guys are hanging on each end of a rope. The rope goes through a pulley. One guy climbs on a rope. what happens to the other guy?
I) If you happen to float in space with an elephant next to you. Far from any gravity.
Would it be easier to push the elephant to get it moving in space than on EArth ?
Remember the mass, the quantity of matter , is the inertia and is the same wherever the elephant happens to be.
THis is because a = ∆V/ ∆t
B) Why a boxer needs to roll over with a punch to lessen the pain ? (same change in motion (velocity) in both cases)
source: Paul Hewitt, conceptual Physics.
6) According to the second law, if the net force is zero (forces can balance each other), what is the change in velocity ? So what is the acceleration ?
7) Suppose a high-flying airplane is flying at a constant speed 900km/h and the thrust of the engines is 80,000 newtons. What is the acceleration of the plane ?
Sketch the situation.
So if you double the force, you ___________ the acceleration
If you triple the net force acting on a body, you ___________ the acceleration
9) A force F is acting on an object of mass m. If you double the mass but keep the force constant
(in magnitude and direction), what will happen to the new change in velocity ∆V? acceleration?
What is the force applied to the object ?
11) Find the acceleration of an automobile of mass 1500kg acted upon by a driving force of P= 2200N @ right
(P = + 2200N) that is opposed by a frictional force of FK= 450N @ left ( FK = - 450N).
Hint Fnet = m a and Fnet = f + F
The motion is opposed by a frictional force of FK=- 2230N. Find the acceleration.
Hint: see 9)
13) An unbalanced force of 25N , F, is applied to a 12-kg mass. What is the acceleration of the mass ?
15) You drag a block of 30g with a force of 5N during 10 minutes. What is the change in velocity ?
hint: convert g to kg and minutes to seconds. Use a = change in velocity / change in time
16) You drag a block of 50g with a force of 5N (to the right) .
A force of friction of 2N is acting to the left.
a) what is the net force ? (right = positive, left = negative)
b) What is the change in velocity of the block after 1 minute ?
hint: use Fnet = m a and a = change in velocity / change in time. convert minutes to seconds and grams to kilograms.
c) What is the change in velocity of the bock after 1 hour ?
d) what is the change of velocity of the block after 1 year ?
e) AFTER 2 YEARS ?
G) if you keep pulling the velocity keeps _______________
h) so can you answer this question:
If one were able to produce and maintain a net force of only 1 Newton on the Queen Mary ocean liner what would be the final speed ?
17) You are pulling on a block with a force of 10N (no friction).
The block was at rest but reaches a velocity of 5m/s. The time elapsed is 10s .
a) Find the mass of the block.
hint: use F = m (change in velocity / change in time)
b) A friction force of 4N@ left is now acting on the block in addition to the 10N@right.
The motion lasts 3 minutes. i) Find the net force acting on the block. ii) Find the acceleration.
hint: use the mass found in a). convert minutes to seconds.
18) Albert the skater, 25kg total mass is propelled by a rocket power. The force F exerted by the rocket can vary.
A) Fill the following table:
B) Suppose now a 50N air resistance (constant) force opposes the motion of Albert.(25kg) F is to the right and the 50N resistance is to the left. Fill the TABLE:
(net force = thrust - air resistance = mass x acceleration)
19)
A) A ball rolls down a uniform slope ramp. The acceleration is:
decreasing ? constant ? increasing?
hint: constant acceleration = constant force (like pull due to gravity)/ Here the gravity is diluted (less than in Free-fall) but stays the same.
If the ramp were steeper, the acceleration would be:
more? the same ? less?
hint; The acceleration you get in free fall (9.8m/s/s) is the maximum acceleration. down a ramp the acceleration is diluted.
When the ball reaches the bottom and rolls along the smooth level surface it:
continues to accelerate? does not accelerate ?
B)
This time a ball rolls down a ramp of varying slope .
The ball's acceleration is greater: at the top ? at the middle? at the bottom?
the speed is greater at:
For this case the speed is greater when the acceleration is the : least ? greatest ?
C) can you draw a crampon which the acceleration of the ball will be very little at the top and progressively greater as it moves down the ramp.
20)
answer this question
(hint: use force x time = mass x change in speed)
21) answer this question
FORCES CAN BALANCE EACH OTHER. A book on a table is at rest, not moving, even if 2 forces are acting on it: the normal force and the weight/
They balance each other, net force = 0. A car moving at a constant speed experiences at least 4 forces: weight = normal force and motrice force = friction.
The net force is 0.
misconception: " Force is action " WRONG. If the net force is 0 there is no acceleration. The object moves at constant speed
or stays at rest.
22) If the net force is 0 , the acceleration is ____.
Acceleration is the change in __________ in 1 second. So if you speed up or slow down you _______ or _________ (negative acceleration).
If your speed increases by 20m/s every second, your acceleration is _______ m/s/s. If your speed decreases by 5m/s every second,
the acceleration is _______ m/s/s (negative number).
If your speed decreases by 30m/s in 5 seconds , the (average) acceleration is ________ m/s/s.
If you speed increases by 10m/s in 10 seconds, the (average) acceleration is _________m/s/s.
If a thrust applied to a car is 100N@right but friction is 10N@left, the net force is _______@ _____.
If the mass of the car is 500kg, the acceleration is __________m/s/s. Meaning, the speed increases
by __________ every __________.
23) Le'ts neglect air resistance. consider 2 objects falling ; a mass of 5kg and a mass of 1 kg.
If you drop them from the CN tower (Toronto) and if you neglect air resistance (they have the same shape)
will they reach the ground at the same time? do they have the same acceleration ? or maybe they don't accelerate?
See if you are right.
The unbalanced force (gravity) acting on 1 kg is ______ N (weight) so its acceleration is _________ m/s/s (use F = m a, solve for a, F is weight)
The unbalanced force acting on 5kg is _________N, so the accelerationn is _______ m/s/s (F = m a with F = weight)
So any free-falling body (no air resistance) fall at the same ________ regardless of the _________.
(remember the penny and the feather in the vacuum tube)
24) When object are moving in a straight line at a constant speed they are said to have a linear u__________ motion
25) Ft = change in momentu. so for the same change in momentum you can have a large F and a small t or the other way around
Why bike helmets are filled with styrofoam ? (imagine crashing on a pole).
CWORKSHEET: REVIEW
video to understand Newton's 3 laws of motion
here is another one:
Newton invented Calculus to explain motions.
His most famous equation is referred as Newton’s second law.
1) Could you find this equation knowing:
- Force (symbol F) causes the velocity to change from an initial value (Vi) to a final value (Vf) . As the force increases, the change in velocity increases.
(∆V = Vfinal - Vinitial =change in velocity )
-The mass or inertia (m) opposes the change in velocity. As m increases, the change in velocity decreases.
- Increasing the time (∆t) during which the force is applied increases the change in velocity.
Call the change in velocity ∆V . (∆V = Vfinal -Vinitial)
Write: ∆V = _________________ Use F, m and ∆t
-----------------------------------------------------------------------------------------------------------------------
2) The second law is now best known as:
The total force (net force) acting on a body is equal to the mass times its acceleration
Or F = _________
a is the _____________ , m is the _____________, F is the ______________
a and F are vector quantities. They have magnitude and direction.
But we will only work in 1D in 10th grade. We will only consider 2 directions:
right and left or up and down. A negative sign shows the down or left direction.
For example: g = -9.8 m/s2 means the acceleration due to gravity is pointing down.
Newton's formula tells us that 1N is the force necessary to accelerate a 1-kg mass at the rate of 1 m/s2
1N is about the force required to lift an apple
Units for F is newton (of kg m/s/s), units for a is m/s2 , units for mass is kg.
F ∆T = m ∆V
----------------------------------------------------------------------------------------------------------
3) Here is another way to understand F = m a . remember that g is the acceleration due to gravity. (acceleration of a free-falling object).
g is 32feet/s/s or 22 mph/s or 10m/s/s. weight is mass x g . Sometime, we express the acceleration in gs.
F = m a can be written as F = (mg) ( a/g). or force = weigth x (acceleration in gs).
That means if you apply 1 pound of force on 1 pound object, the acceleration will be 1 g or 22mph/s .
150 pounds of force on 150 weight, acceleration = 1 g. That's why all objects fall at the same rate if we can neglect friction.
Say you are in your car , at rest, and in 1 second you reach about 20mph. You force you feel on your back is equal to your weight.
If you reach 40mph in 1 second, you feel 2g or twice your weight. You can compute the acceleration astronauts have to undergo
during take off is compute in gs, about 3gs. so they feel 3 times their weight that includes their outfit.
4) DEMONTRATIONS / experiments of thought.
Funny movie to watch: professor Julius Sumner or you can skip it and do the experiments below.
try to answer the questions before he does. Do the experiments. HERE ARE THE DEMONSTRATIONS to do in class.
A) Attach 2 toy cars by a spring. put 1kg in one. stretch the spring. mark the middle. the spring exert the same force on both cars.
Let go the cars. Do they get in the middle at the same time? Which one is faster ? Which one has the smaller inertia ?
(that is which one resists change in motion the least?
So more mass = less acceleration.
So the car with the least mass m will go faster and will reach the middle first. Same force but not the same acceleration.
Mathematically: M a = F = m a
B) Use a round spring scale. attach a mass of 1kg. Read the weight in Newton. weight = mg = ______ N. This is the gravitational force (pull) exerted by the Earth on the mass. This pull stretches the spring and moves the arrow.
You can call it the rest weight. Now quickly move the spring scale upward such as the spring scale is accelerated upward along the vertical.
Call the acceleration of the spring a. While you accelerate the scale read the it. new weight = __________ N
Do you read the same weight ? less ? more ? explain
Because of inertia the mass wants to stay at rest and resists motion. The spring stretches more and the scale reads more.
The pull on the spring is more than the rest weight mg. The pull is : new weight = mg + ma = weight at rest + ma .
with a the acceleration of the spring. Next time you take an elevator, take a bathroom scale with you.
As the elevator moves up (accelerates up), you weight increases by ma. You feel heavier because the bottom of the elevator pushes you, while you want to stay at rest. The force acts on the elevator, not on you. (this phenomenon stops if the elevator moves at a constant speed. When if a frame of reference
that moves at a constant speed, you can't tell if you moving or no. So no weird effect like a change in your rest weight)
MORE ADVANCED:If the elevator accelerates, the weight shown by the scale increases.
In the frame of reference if the elevator, the person is at rest.
THe person feels a force (called pseudo force) pulling him/her down.
This is the same kind of force you feel in a train when it suddenly stops. (or speeds up)
The magnitude of this force is ma . m is the mass of the person and a the acceleration of the elevator.
In the frame of reference of the elevator you have : -ma - mg + T = 0 (T is the support force of the scale
pushing back on you). So T = mg + ma. The scale " feels " the same force T and reads its magnitude.
C) same experience but accelerate the spring downward. Is the reading the same? less ? more ? new weight = __________N
Now the spring is less stretched, the reading is less than the rest weight. new pull = new weight = mg - ma.
If you take an elevator to go down, as the elevator accelerates downward, you feel lighter. You push less on the scale/ (or bottom of elevator)..
(MORE ADVANCED : In the frame of reference of the elevator, you feel a force pulling you up . the magnitude is ma.
In this frame of reference, you are at rest such as : - mg + T + ma = 0 or T = mg - ma . T is the reading on the scale)
D) If you drop the spring scale. The scale is in free fall. What is the reading ?
the spring is not stretch anymore, the mass and the spring are falling at the same rate, the mass is weightless.
a = g so pull = new weight = mg - ma = 0
If you could jump from the table with a bathroom scale attached to your feet, same thing. you would be weightless.
you are both falling at the same rate, you are not pushing on the scale.
Astronauts in space are weightless. (when they orbit the EArth). 2 forces act on them. The force of gravity and the centrifugal force
(the same force you experience in a spinning ride) . The 2 forces balance each other in the the frame of reference of the spaceship orbiting the EArth.`.
so the astronauts feel weightless. Because, they don't need to work against gravity, they experience a loss in muscle.
IN SHORT :
source picture:
From Paul Hewitt book, Conceptual Physics.
The picture shows that if you are in free-fall, the scale does not read anything.
Not because you have no weight but because the scale is falling with you, so you
are not pushing on it anymore. You are : weightless . You are falling with the scale.
astronauts experiencing free-fall. They are said to be " weightless "
The force of gravity is still acting on them but because they fall inside a plane
nothing (like the ground ) is pushing back on them. They don' t feel their weight.
In the international station you are also weightless because you are constantly falling toward the Earth.
The station never reaches the EArth because it also has a tangential motion.
HERe is an expected consequence of zero gravity
E) Here in an experiment to understand better the weightless phenomenon. Get a Styrofoam cup and make holes at the bottom.
Fill it with water. Of course the water will leak because of the pull of gravity. But now drop the cup full of water. (above a sink).
the cup and the water are in free-fall and the water does not leak !
F) get 2 spheres of different mass. In free-fall, they both the ground at the same time. They have the same acceleration because:
small mass: F1 = m a1 (newtons 2nd law) and F1 = m g (force = pull due to gravity) so a1 = m g / m = g
large mass: F2 = m a2 and F2 = Mg so g2 = Mg / M = g
Do the experiment with a feather and a penny in a vacuum.
G) Imagine 2 little girls. they both weighs 70 pounds. one is standing up a hill and the other one at the bottom, ready to read a spring scale/
The top girl jumps on the spring scale. The reading is less than 70 ? more ? 70 pounds ?
The scale is pushing back on you, the reaction is your " new weight ".
There is a way to estimate how much push you get.(your new weight) Your energy on the hill = weight x height. (called potential energy).
(energy is force applied x distance it is applied, here the force is the pull due to gravity, the distance is the height).
In a first approximation, we can say your energy is conserved (neglecting loss of energy to heat and noise) .
so real weight x height = force on spring scale x distance the spring is compressed. Say you jump 1 meter (about 1 yard)
and the spring moves by about 10cm (stiff spring) then you weigth will be multiplied by 10. If you jump of the floor, it hurts more
because the floor hardly moves (by a few micro meters) so you will feel a greater force. It is a force multiplier.
H) 2 guys are hanging on each end of a rope. The rope goes through a pulley. One guy climbs on a rope. what happens to the other guy?
I) If you happen to float in space with an elephant next to you. Far from any gravity.
Would it be easier to push the elephant to get it moving in space than on EArth ?
Remember the mass, the quantity of matter , is the inertia and is the same wherever the elephant happens to be.
---------------------------------------------------------------------------------------------------------------------------------------------
5)
A) You increase the speed of a ball you are throwing by keeping it longer
in
THis is because a = ∆V/ ∆t
B) Why a boxer needs to roll over with a punch to lessen the pain ? (same change in motion (velocity) in both cases)
source: Paul Hewitt, conceptual Physics.
6) According to the second law, if the net force is zero (forces can balance each other), what is the change in velocity ? So what is the acceleration ?
7) Suppose a high-flying airplane is flying at a constant speed 900km/h and the thrust of the engines is 80,000 newtons. What is the acceleration of the plane ?
Sketch the situation.
So if you double the force, you ___________ the acceleration
If you triple the net force acting on a body, you ___________ the acceleration
9) A force F is acting on an object of mass m. If you double the mass but keep the force constant
(in magnitude and direction), what will happen to the new change in velocity ∆V? acceleration?
What is the force applied to the object ?
11) Find the acceleration of an automobile of mass 1500kg acted upon by a driving force of P= 2200N @ right
(P = + 2200N) that is opposed by a frictional force of FK= 450N @ left ( FK = - 450N).
Hint Fnet = m a and Fnet = f + F
The motion is opposed by a frictional force of FK=- 2230N. Find the acceleration.
Hint: see 9)
13) An unbalanced force of 25N , F, is applied to a 12-kg mass. What is the acceleration of the mass ?
15) You drag a block of 30g with a force of 5N during 10 minutes. What is the change in velocity ?
hint: convert g to kg and minutes to seconds. Use a = change in velocity / change in time
16) You drag a block of 50g with a force of 5N (to the right) .
A force of friction of 2N is acting to the left.
a) what is the net force ? (right = positive, left = negative)
b) What is the change in velocity of the block after 1 minute ?
hint: use Fnet = m a and a = change in velocity / change in time. convert minutes to seconds and grams to kilograms.
c) What is the change in velocity of the bock after 1 hour ?
d) what is the change of velocity of the block after 1 year ?
e) AFTER 2 YEARS ?
G) if you keep pulling the velocity keeps _______________
h) so can you answer this question:
If one were able to produce and maintain a net force of only 1 Newton on the Queen Mary ocean liner what would be the final speed ?
17) You are pulling on a block with a force of 10N (no friction).
The block was at rest but reaches a velocity of 5m/s. The time elapsed is 10s .
a) Find the mass of the block.
hint: use F = m (change in velocity / change in time)
b) A friction force of 4N@ left is now acting on the block in addition to the 10N@right.
The motion lasts 3 minutes. i) Find the net force acting on the block. ii) Find the acceleration.
hint: use the mass found in a). convert minutes to seconds.
18) Albert the skater, 25kg total mass is propelled by a rocket power. The force F exerted by the rocket can vary.
A) Fill the following table:
| Thrust F | acceleration |
| 100N | 4 m/s/s |
| 200N | |
| 10m/s/s |
B) Suppose now a 50N air resistance (constant) force opposes the motion of Albert.(25kg) F is to the right and the 50N resistance is to the left. Fill the TABLE:
(net force = thrust - air resistance = mass x acceleration)
| Thrust F | acceleration |
| 50N | 0 ms/s |
| 100N | |
| 200N |
19)
A) A ball rolls down a uniform slope ramp. The acceleration is:
decreasing ? constant ? increasing?
hint: constant acceleration = constant force (like pull due to gravity)/ Here the gravity is diluted (less than in Free-fall) but stays the same.
If the ramp were steeper, the acceleration would be:
more? the same ? less?
hint; The acceleration you get in free fall (9.8m/s/s) is the maximum acceleration. down a ramp the acceleration is diluted.
When the ball reaches the bottom and rolls along the smooth level surface it:
continues to accelerate? does not accelerate ?
B)
This time a ball rolls down a ramp of varying slope .
The ball's acceleration is greater: at the top ? at the middle? at the bottom?
the speed is greater at:
For this case the speed is greater when the acceleration is the : least ? greatest ?
C) can you draw a crampon which the acceleration of the ball will be very little at the top and progressively greater as it moves down the ramp.
20)
answer this question
(hint: use force x time = mass x change in speed)
21) answer this question
FORCES CAN BALANCE EACH OTHER. A book on a table is at rest, not moving, even if 2 forces are acting on it: the normal force and the weight/
They balance each other, net force = 0. A car moving at a constant speed experiences at least 4 forces: weight = normal force and motrice force = friction.
The net force is 0.
misconception: " Force is action " WRONG. If the net force is 0 there is no acceleration. The object moves at constant speed
or stays at rest.
22) If the net force is 0 , the acceleration is ____.
Acceleration is the change in __________ in 1 second. So if you speed up or slow down you _______ or _________ (negative acceleration).
If your speed increases by 20m/s every second, your acceleration is _______ m/s/s. If your speed decreases by 5m/s every second,
the acceleration is _______ m/s/s (negative number).
If your speed decreases by 30m/s in 5 seconds , the (average) acceleration is ________ m/s/s.
If you speed increases by 10m/s in 10 seconds, the (average) acceleration is _________m/s/s.
If a thrust applied to a car is 100N@right but friction is 10N@left, the net force is _______@ _____.
If the mass of the car is 500kg, the acceleration is __________m/s/s. Meaning, the speed increases
by __________ every __________.
23) Le'ts neglect air resistance. consider 2 objects falling ; a mass of 5kg and a mass of 1 kg.
If you drop them from the CN tower (Toronto) and if you neglect air resistance (they have the same shape)
will they reach the ground at the same time? do they have the same acceleration ? or maybe they don't accelerate?
See if you are right.
The unbalanced force (gravity) acting on 1 kg is ______ N (weight) so its acceleration is _________ m/s/s (use F = m a, solve for a, F is weight)
The unbalanced force acting on 5kg is _________N, so the accelerationn is _______ m/s/s (F = m a with F = weight)
So any free-falling body (no air resistance) fall at the same ________ regardless of the _________.
(remember the penny and the feather in the vacuum tube)
24) When object are moving in a straight line at a constant speed they are said to have a linear u__________ motion
25) Ft = change in momentu. so for the same change in momentum you can have a large F and a small t or the other way around
Why bike helmets are filled with styrofoam ? (imagine crashing on a pole).
CWORKSHEET: REVIEW
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