Force, mass and acceleration: the trolley run
Pull a trolley with different forces and loads, read its ticker tape, and discover how force and mass change its acceleration.
Core concept
Acceleration increases with force and decreases with mass (a = F ÷ m)
Topic: Force and motion
An unbalanced force: A push or a pull. Forces can start, stop or turn things. All key words makes an object speed: How far something travels in a certain time, like kilometres per hour. All key words 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: How much matter something has, measured in grams or kilograms. It is the same everywhere. All key words: 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
- Keep the mass at 1 kg. Run the trolley with at least three different forces and record each run.
- Keep the force the same. Add bricks to change the mass, and record at least three runs.
- 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.