10. Acceleration Due to Gravity

Question 1

Define the term freefall

Answer 1

When there is gravity acting on an object and nothing else - the motion of an object undergoing an acceleration of ‘g’

Question 2

What direction does ‘g’ act?

Answer 2

Vertically downwards

Question 3

What is the magnitude of ‘g’?

Answer 3

9.81 m/s^2 but can vary at different points on the Earth’s surface

Question 4

What is the only force acting on an object in freefall?

Answer 4

Weight

Question 5

How can the idea that all objects fall at the same rate be explained?

Answer 5

Using Newton’s 2nd law of motion

Question 6

What does Newton’s 2nd law of motion explain?

Answer 6

That acceleration is independent of mass

Question 7

Name the 3 cases of freefall

Answer 7

1. No initial velocity
2. An initial velocity upwards (object is projected up in the air)
3. An initial velocity downwards (object is thrown downwards)

Question 8

Describe the steps for the practical to determine ‘g’ using freefall

Answer 8

1. Set up the equipment: electromagnet, ball bearing, switch, timer and trapdoor
2. Measure the height, h, from the bottom of the ball bearing to the trapdoor
3. Flick the switch to simultaneously start the timer and disconnect the electromagnet, releasing the ball bearing
4. The ball bearing falls, knocking the trapdoor down and breaking the circuit, which stops the timer
5. Record time, t, shown on timer
6. Repeat experiment three times and average the time taken to fall from this height
7. Repeat experiment but drop ball from different heights
8. Use these results to find g using a graph

Question 9

What is the most significant source of random error in the practical?

Answer 9

Measuring h because the ruler has an uncertainty of ±1 mm

Question 10

Why is a small and heavy ball used?

Answer 10

To assume air resistance is so small it can be ignored

Question 11

Why is this method better than using a stopwatch and dropping the ball by hand?

Answer 11

There is a smaller uncertainty because a human’s reaction time does not need to be taken into consideration

Question 12

What error can occur due to the use of a computer?

Answer 12

Systematic error - if there is a delay in the switch or timing mechanism

Question 13

How do you plot the results?

Answer 13

x-axis = time taken to fall squared in s^2
y-axis = height in m

Question 14

What does the gradient show on the graph?

Answer 14

1/2 g

Question 15

How do you work out ‘g’?

Answer 15

Find the gradient and then double it