1. Mass & Speed
D. Crowley, 2008

2. Wednesday, April 19, 2017
Mass & Speed
To be able to describe how the mass of an object can affect its speed

3. Mass & Speed How do you think mass affects speed?
Do objects with a bigger mass accelerate faster / slower than objects with a smaller mass?
Discuss how you could carry out an experiment to investigate this…

4. Mass & Speed
In order for this to be an accurate experiment we need to use objects which look identical, yet have a different mass
This is because we want the objects to experience the same conditions - i.e. the same amount of friction (air resistance and the same amount of contact with the surface)
We also need to consider how we can measure the objects speed - if it reaches too fast a speed, our reaction times will become very significant…

5. Mass & Acceleration
Using margarine tubs of the same size, we can use a force meter to push them a known distance and measure how quickly it took to cover this distance
The force we use to push the margarine tub needs to be kept constant
Then we can work out their speed (distance  time)
We can then repeat this, using different masses added to the tub
Force
Start point
End point

6. Experiment
Measure the distance between a start and finish line across the table using a meter ruler (the distance should be around 50cm)
Using a margarine tub, push it using the force meter from the start line to the finish
Time how long it takes to cover this distance
Repeat this 3x (recording the time taken to cover the distance)
Repeat the experiment exactly for the margarine tub containing different masses (0g, 10g, 20g, 30g, 40g and 50g)
Force
Start point
End point

7. Time taken to complete course (sec)
Results
Object
Time taken to complete course (sec)
Measurement 1
Measurement 2
Measurement 3
Average 0g
(tub only)
10g
20g
30g
40g
50g
Then work out the average speed of both objects (distance  time)

8. Acceleration = Force  Mass
Findings
Hopefully you have found that a bigger mass took longer to cover the distance – this is because it takes longer to accelerate
It takes longer to accelerate as more force is needed to move the larger object
When we keep the force constant the heavier object takes longer to accelerate
Acceleration = Force  Mass

9. Acceleration = Force  Mass
Start point
End point
Mass x 2
Force
Start point
End point
If force is constant, then a greater mass takes much longer to accelerate
Acceleration = Force  Mass

10. Force
What happens when you drop two objects of different mass? Does the heavier object fall faster?
Both objects fall at the same speed (a bigger mass does not mean more speed)
In other words, drop an elephant and a mouse and they will hit the floor at the same time (if frictional forces are not interfering)
Even though there is more force on the elephant pulling it down (as there is more mass) it takes much more force to accelerate it (so the forces effectively cancel each other out) and the elephant and mouse hit the floor at exactly the same time

11. Force
The elephant with 2x mass has a force 2x bigger, but it takes 2x more force to accelerate it, so the two cancel each other out, and both fall at the same speed

12. Galileo
Apollo 15 landed on the moon, and proved this is correct…

13. Earth Would a hammer and a feather fall at the same speed on Earth?
On Earth the hammer would fall much faster, due to air resistance (the air would slow the feather down considerably)