Investigating Motion

You can investigate how mass and force affect acceleration

  • Set up the apparatus shown below. Set up the trolley so it holds a piece of card with a gap in the middle that will interrupt the signal on the light gate twice. If you measure the length of each bit of card that will pass through the light gate and input this into the software, the light gate can measure the velocity for each bit of card. It can use this to work out the acceleration of the trolley
  • Connect the trolley to a piece of string that goes over a pulley and is connected on the other side to a hook
  • The weight of the hook and any masses attached to it will provide the accelerating force, equal to the mass of the hook x acceleration due to gravity
  • The weight of the hook and masses accelerates both the trolley and the masses, so yopu are investigating the acceleration of the system
  • Mark a straight line on the table the trolley is on, so that the trolley always travels the same distance to the light gate
  • Place the trolley on the straight line, holding the hook so the string is taut and release it
  • Record the acceleration measured by the light gate as the trolley passes through it. This is the acceleration of the whole system

To investigate the effect of mass, add masses to the trolley one at a time to increase the mass of the system. Don’t add masses to the hook, or you’ll change the force. Record the average acceleration for each mass

To investigate the effect of force, you need to keep the total mass of the system the same, but change the mass on the hook. To do this, start with all the masses loaded onto the trolley, and transfer the masses to the hook one at a time, to increase the accelerating force. The mass of the system stays the same as you’re

only transferring the masses from one part of the system to another. Record the average acceleration for each force

Newton’s second law can explain the results

  • Newton’s second law can be written as F=ma. Here F=weight of the hanging masses, m=mass of the whole system and a=acceleration of the system
  • By adding masses to the trolley, the mass of the whole system increases, but the force applied to the system stays the same. This should lead to a decrease in the acceleration of the trolley, as a=F/m
  • By transferring masses to the hook, you are increasing the accelerating force without changing the mass of the whole system. So increasing the force should lead to an increase in the acceleration of the trolley