7: Acceleration

  • A toy car is attached to a piece of string.

  • The string is looped around a pulley

  • The other end of the string is attached to a 100g mass.

  • The weight of the mass will provide the force acting on the toy car.

  • We also need a timer

  • On the desk, we draw chalk lines at equal intervals (e.g every 10cm)

We now hold the toy car at the starting point.

When ready, let go of the car. Because of the resultant force acting through the string, the car will accelerate along the bench. We need to record the time that the car passes each distance marker.

If the car is moving rapidly, then it will be difficult to record an accurate time.

A better way to do this is to record the experiment on a phone.

We can then play the video back and record the times accurately.

We then repeat the experiment multiple times, but in each case we decrease the mass on the end of the string.

This means that the weight (force) is decreasing each time.

We are investigating the effect of changing the force on the acceleration of an object, while keeping the mass of the object constant.

In this experiment, the object is not just the toy car.

It is the toy car, the string and the mass on the end of the string. This is because they are all attached to each other.

So we count them all as the object.

This means that if we take away some of the mass from the end of the string, we then have to transfer that mass onto the toy car. By doing so, we keep the overall mass of the object the same.

Newton’s second law of motion tells us that the acceleration of an object is proportional to the force applied.

The force in this case is the weight of the mass on the end of the string.

We should find that the acceleration of the toy car is proportional to the mass on the other end of the string.

We can use the same equipment to investigate how varying the mass of an object affects the acceleration produced by a constant force. In this case, we keep the force constant (e.g using a 100g mass on the end of the string).

We now attach a mass to the toy car (eg 200g)

Just as before, we record the car as it accelerates along the bench.

We repeat the experiment increasing the mass attached to the toy car.

Newton’s second law tells us that the acceleration of an object is inversely proportional to the mass of the object.

With this experiment, we should find that as we increase the mass of the toy car, the acceleration decreases.