Core Practical 1 - Determine the Acceleration of a Freely-Falling Object

Question 1

What is the aim of this core practical?

Answer 1

To Determine the Acceleration of a Freely-Falling Object

Question 2

Method with the ELECTROMAGNET requires what equipment?

Answer 2

• electromagnet
• ball bearing
• switch
• timer
• trapdoor
• metre rule

Question 3

How does this practical work?

Answer 3

Measure height from the bottom of the ball bearing attached to electromagnet (which is connected to a power supply) all the way to the trapdoor.
Flick the switch to remove the power from the electromagnet and essentially give it to the timer. The timer will start.
When the ball reaches the trapdoor, circuit is broken and the timer stops. Record t and h.

Question 4

Is this method appropriate to have repeated readings?

Answer 4

Yes, repeat 3 times for each height and then for different heights. Remember to work out the mean.

Question 5

What are we plotting with this method?

Answer 5

t^2 against h (from a suvat) (t = y and h = x)

Question 6

What is the gradient?

Answer 6

m = 2/g where m is the gradient

Question 7

Additional actions that can be taken to ensure accuracy and precision?

Answer 7

• use a small and heavy ball bearing so we can assume the air resistance is really small
• use a larger distance to reduce percentage uncertainty in our time measurement (caused by the resolution of the timer)
• use lower current to reduce magnetism of the electromagnet and hence the delay between pressing switch and releasing ball would be smaller
• use a computer to record time and automatically release ball can measure time with a smaller uncertainty

Question 8

What is the second method for this practical?

Answer 8

Free-fall plasticine or a card

Question 9

What is the equipment required for method 2?

Answer 9

• card or plasticine
• clamp
• metre rule
• light gate
• data logger or computer (not necessary)

Question 10

What is the procedure for method 2?

Answer 10

Clamp a thin piece of card to the top and measure height, h, from the centre of card to the top
of the light gate using a ruler clamped parallel using a set square
• Release the card from the top
• Light gate at the bottom will record the time for which the card passes through
o Calculate instantaneous final speed, v, of the card as:
v =
length of card/time
• Repeat procedure 3 times, discard anomalies and calculate mean v for the given h
• Vary h and record the respective values of v

Question 11

What would we plot for method 2?`

Answer 11

v^2 against h (v = y and h = x)

Question 12

What is the gradient for method 2?

Answer 12

m = 2g

Question 13

What is a big problem with this method and how can it be tackled?

Answer 13

Path taken by card is not directly vertical introducing uncertainty in the measure of h: attach
blue tack to the bottom tips of the card for stability

Question 14

What is a big advantage of this practical?

Answer 14

Reaction time has no effect on results as light gate is used to measure time (and method 1 too)