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Grades 7, 9, and 10 Intermediate About 20 min Version 1 Awaiting review Premium

Force, mass and acceleration: the trolley run

An unbalanced force makes an object speed up, slow down or change direction. How quickly its velocity changes is its acceleration, measured in metres per second per second (m/s²). Newton's second law says the acceleration is proportional to the force and inversely proportional to the mass: a = F ÷ m, or F = m × a. A ticker timer marks a paper tape every 0.1 s; when the dots get further apart, the trolley is speeding up.

What you will learn

  • Describe how a bigger force changes the motion of a trolley.
  • Show that acceleration is proportional to force when mass stays the same.
  • Show that acceleration decreases when mass increases, and use F = m × a.

Before you start

  • Know that speed = distance ÷ time.

Materials

  • Bricks of 0.5 kg to load the trolley
  • Ticker tape

Equipment

  • Trolley and runway, friction-compensated
  • Ticker timer (50 dots per second, shown here as one dot every 0.1 s)
  • Force meter or elastic cords to give a steady pull

Procedure

  1. Keep the mass at 1 kg. Run the trolley with at least three different forces and record each run.
  2. Keep the force the same. Add bricks to change the mass, and record at least three runs.
  3. Look at the graph of acceleration against force.

How this simulation is simplified

  • The runway is tilted just enough to cancel friction.
  • The pulling force stays the same during the run.