HOW MASS IS RELATED TO INERTIA ?  FILL BLANKS FOR FULL CREDITS



You might know that, if we neglect air resistance, all bodies fall at the same rate regardless of their mass. At the same rate means they fall with the same _________ (force ? hamster ? acceleration ? distance ? )                        So a penny and a father dropped in a vacuum tube will reach the ground at the same_______ (we did this experiment in class ?)  The only force acting of free-falling object is the _________.  Let’s see why this is true.  (why the acceleration of __________ bodies  is the same no matter the mass (check title) )
Newton 2^nd law says : F = __________ . m is the mass of the body experiencing the force F and a the acceleration of the body. If an object is in free-fall, the only force acting on it is the ________= m g   . g  is the acceleration due to gravity or 9.8m/s/s. (in m/s/s). In  F = ma substitute  F for the weight = mg .                        you get ___ = ____ or ____ = ______ (cross-out m). So the acceleration of free-falling bodies does not depend on the _________.  Look at the picture above. If you roll a bottle down a slope, there is no friction because the bottle is rolling and not sliding. So even if the acceleration is diluted (not falling straight down) the same concept can be applied and no matter the mass of the bottle, the ___________ is the same.  Not matter the mass, the bottle reaches the floor with the same __________-. (cookie ? pressure ? speed ? ). In our experiment, the speed is called a controlled variable (you keep it the _________ ). The mass of the bottle will vary. This will be our ____________ variable (cookie ? manipulated or independent ? accelerated ? ).   
A block will be placed on the floor and will stop the bottle. Indeed, the _________ force between the block and the ground opposes the motion of the system block + bottle. The net force acting on the system is not zero along the horizontal so the system will ____________ and stop. The bottle will cover a distance d.
We want to find out if increasing the mass m of the bottle will increase or decrease (or not changing)  the distance covered by the bottle after it collides with the block. What do you think? as the mass of the bottle increases, the distance the bottle covered before stopping should increase too ? or decrease ? why?


hint: In other words, as you increase the mass (inertia) of the bottle, will it harder or easier for the block to stop it ? _________________________________________________________________________
So the mass of the bottle  is our __________ variable and the distance is our ____________ variable (cookie ? responding or dependent ? manipulated ? independent ? )

PROCEDURE (you need a small glass bottle , a block of wood (or cup), a ramp, meter stick, graduated cylinder)

1) Place the ramp on 1 big Physics book. You want to make sure your bottle gets enough momentum when it leaves the ramp. Build 2 tracks with 2 meter sticks on the floor. See picture. Secure with tape. The bottle needs to go in a straight line but should not touch the track. 

3) Mark the middle of the ramp. This will be the starting point for the bottle to roll down.
4) Place a small piece of masking tape on the floor in line with the center of the ramp at a distance of 10 cm from the base of the ramp. This is the starting point for the block  in each trial. 

5) Using a graduated and a funnel, carefully pour 100ml of water into the bottle. Close the bottle tightly and dry the outside of the bottle with paper towel. Wipe up any spills immediately. Place the block at its starting point, with its closest point to the ramp touching the piece of masking tape.  
Let the bottle rolls from the starting point. When the bottle and the block  have stopped moving record the distance covered by the block . (from starting point)
 Repeat 5 times and find the average. Record in TABLE1. 

5) Add 100mL and repeat procedure. Record in TABLE 1.

6) repeat5)

TABLE (if 500ml does not fit, take 450  or less – also 100ml = 100g of water )

volume water (ml =g)	distance (cm) trial1	distance (cm) trial2	distance (cm) trial3	distance (cm) trial4	distance (cm) trial 5	distance (cm) average
100ml = 100g	__________	__________	__________	__________	__________	__________
200g	__________	__________	__________	__________	__________	__________
300g	__________	__________	__________	__________	__________	__________
400g	__________	__________	__________	__________	__________	__________
500g?_________	__________	__________	__________	__________	__________	__________

ANALYSIS

1)      The independent variable (manipulated)  is ___________________, the dependent variable is ________________ (responding). (refer to 1^st paragraph).


2)       The data show that as the inertia (mass) of the bottle increases , the distance the bottle moves the block  on the floor ______________.
 
3)      The bottle stops because of the _______ force between the block and the ________. This friction force acts on the system bottle-block and the bottle eventually _________. The force caused a change in the _______ of the bottle.  We suppose here that this  force is the same (constant) no matter the mass of the bottle. This is because the friction force between the block and the ground only depends on the ________ of the block. We neglect the friction between the bottle and the ground because the bottle is _________ and not _______. (refer to 1^st paragraph) . So the force that causes the bottle to stop (friction block/ground) is __________ (stays the same) and is called a __________ variable.


4)      So why the distance increases as the mass increases: As the mass of the bottle increases, its __________ increases and it is harder for the __________ to stop the bottle. Therefore, the cup and bottle will cover a larger __________. 


5)      Now we want to investigate what kind of direct relationship we have between the distance and the mass.  What do you think ?
6)      Fill the following table:

x= mass water (g)	y = distance (cm)

 7) Plot distance traveled (y) vs mass water (x). Trace the best fit curve (line). title + labels of axis. go through origin. use graph paper and ruler. be consistent with scales.


8) Explain why we can neglect the friction between the bottle and the ground and not the friction between the block and the ground.

9) Explain what caused the system block-bottle to stop ?
 
 
10) What is a controlled  variable (during an experiment) ?
 
 
11) what are the 2 controlled variables in this lab (at least the ones I mentioned )
 
 
12) What could you do to increase the speed of the bottle before it collides ?
 
 
13) What are the manipulated variable ? and the responding variable ?
    

14) Find the slope of the graph (decimal form) slope = _______ cm / g.

 

15) Find the equation of the line y = __________________.

 

16) using the equation , predict the distance  covered by a 250g bottle before it stops

 

17) The linear relationship between the distance and the mass tells you that if you double the mass (inertia) of the bottle, then you _________ the distance. If you triple the mass, you __________ the distance.

 

18) the experiment also shows that there is a linear relationship between the mass of the bottle (or any object) and its kinetic energy. Kinetic energy is the energy of motion. If an object has kinetic energy it can move other object and can cause damage. The formula for kinetic energy is 0.5 x mass x (speed)²  . The bottle gains kinetic energy along the slope and can push the block over a distance.  If there is a linear relationship between the distance  and the kinetic energy, it means: is 0.5 x mass x (speed)² = F x (distance block moves)

F is just a constant. (it is actually the constant frictional force). So the above formula shows that if you double the mass you _________ the distance for a given speed at the end of the slope. (speed is a _________ variable)

But the speed in the formula is squared. That means if you double the speed (by increasing the angle between the plane and the floor, or by letting the bottle go higher up) , the distance is not multiplied by 2 but by ______ !!!  (squared).

 

Let’s see an application of that formula. A car moving at a speed of 30 mph suddenly brakes. It slides and stops. (the friction force was at work to stop the car). the skid marks are 5 m long. If the car was going at 60mph (twice that much), what is the distance of the skid marks ?

19) What did you learn from this lab ? be specific.