cahier physique - physics workbook

INTRODUCTION - READ AND FILL THE BLANK FOR FULL CREDITS.
BANK: same - gravity - velocity - pull - time - force - acceleration

In this lab we will neglect friction. A car toy will roll down an incline plane and we will try to compute its acceleration using the equations of motion. It is the _______ of gravity that pulls the cars down. However, the car is not falling vertically. So the pull of _______ is diluted because of the slope of the plane. More gentle is the slope, more diluted is the ______ and smaller is the acceleration. You should get an acceleration smaller than 9.8m/s. Since the force of gravity stays constant along the plane, the _______________ should also stays constant along the plane. The car gets faster but the acceleration stays the same. So Whether you let go your car at the top of the incline or in the middle or at the end, you should find the ___________ acceleration.

the general formula for acceleration is: a = change in _________ / change in __________

PART1 = 1 physics book high
PART 1: PROCEDURE

1)

Use the meter stick and masking tape to mark a starting line (0cm) at the top of the ramp, followed by marks 15, 30,45, 60, 75, 90, 105(if the ramp is long enough), 120 (if the ramp is long enough). If 105 is too large make up your own mark so you
have 1 or 2 more marks after 75cm. You can change the marks if you think yours are better.
!!! don't make the mark on the way of the car. It will slows it down. Put the mark on the side.

2) position the ramp so the slope is gentle. Use a Physics book.

3) Place the car at the top of the ramp and release it. You should use a small ruler to release it. position the ruler in the front of the car and quickly lift it when your friend says go. Use the stopwatch to time. How long it takes the car to reach the 15cm mark. Record your time in TABLE1.

TABLE 1
distance (cm)	time(sec)	average velocity (cm/sec)	Final velocity (cm/sec)	acceleration (cm/sec)
0	0	_____	_____	______
15	______	______	______	______
30	______	______	______	______
45	______	______	______	______
60	______	______	______	______
75	______	______	______	______
90	______	______	______	______
--	______	______	______	______
---	______	______	______	______

4) Repeat step3 for each of the remaining distances marked on the ramp.

ANALYSIS PART 1 (do it at home or when you are done collecting data. move to PART 2)

1) Here are the 5 big fives that we used in class:
UNDERSTAND: HERE V1 = 0 for t=0 (the initial velocity is 0, the car starts at rest) and V2 is the final velocity
EQUATION 1) average velocity Vav = d / t (total displacement over total time).
EQUATION 2) or Vav = (V1 + V2 ) (acceleration is constant)
EQUATION 3) a = (V2 - V1) /t or (acceleration = change in velocity over change in time)
or V2 = V1 + at
.
EQUATION 4) d = V1 t + at² / 2 with a the acceleration, V1 the initial velocity
EQUATION 5) : V2² = V1² + 2ad

For each time measurements that you made calculate:
A) The average velocity Vav. (use equation 1)
report in TABLE1
B) The final velocity V2. Use V1=0 , the equation 2 and, your answer in A)
report in TABLE1
C) the acceleration a. Use V1 = 0, equation 3.
report in TABLE1

2) Do you get about the same acceleration? convert to m/s. is it below the acceleration of objects in free-fall ? (9.8m/s/s)

PART2 = 2 physics book high
PROCEDURE part II

REPEAT PART1 for 2 physics high.
If the car goes too fast, you can choose less points along the track.
Like 30cm, 60cm, 90cm. REPORT in TABLE2

TABLE 2
distance (cm)	time(sec)	average velocity (cm/sec)	Final velocity (cm/sec)	acceleration (cm/sec)
0	0	_____	_____	______
30	______	______	______	______
________	______	______	______	______
____	______	______	______	______
____	______	______	______	______
____	______	______	______	______
____	______	______	______	______
--	______	______	______	______
---	______	______	______	______

ANALYSIS PART II - do this part at home and move to PART III

For each time measurements that you made calculate:
A) The average velocity Vav. (use equation 1)
report in TABLE2
B) The final velocity V2. Use V1=0 , the equation 2 and, your answer in A)
report in TABLE2
C) the acceleration a. Use V1 = 0, equation 3.
report in TABLE2

2) Do you get about the same acceleration for any measurement? convert to m/s.
Is it below the acceleration of objects in free-fall ? (9.8m/s/s)

3) is the acceleration larger than in part 1 ?

PART3: acceleration due to gravity

PROCEDURE

Let's try now to estimate the acceleration due to gravity.
Tape 3 meter sticks along the wall. You will have to climb on a table. Be careful not to fall.
Drop a marble from 3 meters high and find the time for the marble to reach the ground.
The person on the table will drop the marble and shout GO. As soon as you hear the click
of the marble reaching the ground you stop the watch.
Do it 5 times and average the time :

time (s)

____

_____

average time = t_av = _____ seconds.
Then use equation 4 to find the acceleration.
You have V1=0, d=3m, t=t_av.
solve for a. a = _____ m/s/s are you close ?