Core practical: force, mass and acceleration

A light gate sends a beam of light to a sensor. When a card on the trolley passes through, it breaks the beam and a data logger records the time.
speed = length of card ÷ time the beam is blocked
With two light gates (or a double card), you get two speeds and the time between them, so:
a = (v − u) ÷ t
Light gates remove human reaction time from the timing, so they are more accurate than a stopwatch.

1. Put a trolley on a runway (slightly tilted to cancel out friction) with a string over a pulley to a hanging mass.
2. The weight of the hanging mass is the accelerating force.
3. Changing the force: move masses one at a time from the trolley to the hanger. This keeps the total mass being accelerated the same.
4. Changing the mass: add masses to the trolley but keep the hanging mass the same.
5. Record the acceleration each time and repeat to find means.

F = m × a
For a fixed mass, acceleration is directly proportional to the force: a graph of a against F is a straight line through the origin.
For a fixed force, acceleration decreases as the mass increases.
Safety: put something soft at the end of the runway to catch the trolley, and keep feet clear of falling masses.