Newton's Second Law
Forces and Motion

Modelling braking

Classroom Activity for 11-14 Supporting Physics Teaching

What the Activity is for

You can build this model with pupils to show how the forces deliberately applied to the car by operating the accelerator or the brake lead to the car speeding up or slowing down. Two different models are presented. Both give the same behaviour.

What to Prepare

  • either one computer, connected to a large display, running the modelling program VnR
  • or a collection of computers running the modelling program VnR, so that pupils can work in groups of two or three
  • the models (see below)

What Happens During this Activity

Either you or the pupils build the models shown. The reconstruction given here gives the salient points, but you need not follow the sequence slavishly. In particular, you can adapt the starting points, perhaps giving the pupils the variables and asking them to connect them together after working through the appropriate story.

The first model emphasises the calculation of differences in the forces acting to find one force that has the same effect as all of the forces applied separately. This one force then changes the speed.

The second model shows how the forces contribute to the kinetic store of energy. This in turn affects the speed. The accelerator always contributes positively, the drag and the brakes always negatively.

If you choose to build the model up with the class, you may find it a good strategy to have a volunteer to do the keyboarding and pointer driving for you, allowing you to concentrate on running the discussion with the class.

A good way to work is for you to build up parts of the model, then allow the pupils to build, or at least be in the driving seat for, the remaining significant linking steps.


Download the models for this activity.

Newton's Second Law
is expressed by the relation F=ma
can be used to derive Kepler's First Law
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