19 Measuring speeds on a runway

Read

When a trolley or toy car moves freely down a slope, it appears to get faster as it nears the bottom. In this experiment, you will measure the speed of the trolley at different points along an inclined plane by moving the position of the Light gate.

An interrupt card fitted to the car will break the Light gate’s beam. The software records the time that the beam is broken by the card. The length of the card is entered in the software, which will then calculate the speed.

Speed = Distance (length of card) Time (taken for the card to go through the Light gate)

What you need

 1 x EasySense logger  1 x Light gate  Trolley and inclined plane OR toy car and ramp with marks at 5 cm intervals  Card 3 cm long, with a marked centre point fitted to the top of the trolley or toy car

What you need to do

1. Assemble the apparatus. Connect the Light gate to input A on the data logger. 2. Fix the Light gate at position 1 on the inclined plane (5 cm from the end). 3. Select Timing from the Home screen, from the recording wizard set up as below:

4. Select Start . 5. Align the centre mark of the card on the trolley with the start line and release the trolley. The speed will be shown on the graph.

If any mishaps occur select the incorrect reading, Delete then repeat the reading. 6. Place the Light gate at the second position on the slope (10 cm from the end), and repeat the experiment. 7. Repeat with the Light gate at position 3, 4 and 5 on the slope.

Questions

 Compare the speed values at 5 cm with those at positions 2, 3, 4 and 5. Is there a pattern in the way speed changes with distance?

Extensions

 Repeat the experiment with the slope at different heights. Does the shape of the graph change?  Does the mass of the trolley or car change the result? Load masses on to the trolley to find out.

Speed/Velocity At A Single interrupt card Enter the length of the interrupt card