Forces - Forces and their Effects

Knowing about forces is much more than just learning a few ideas for your physics GCSE!

Unbalanced forces can cause changes to the shape or motion of an object - they can move in a straight line at a constant speed when the forces are balanced or change their shape, speed and / or direction (accelerate or decelerate). Graphs can be used to describe the movement of an objects, the two that you need to learn about are distance-time graphs and velocity-time graphs. For your GCSE, you need to be able to use your skills, knowledge and understanding to interpret data from tables and graphs relating to speed, velocity and acceleration in a wide variety of contexts. Two of the main contexts they use are about cars and skydiving.

For cars, you need to evaluate the effects of alcohol and drugs on stopping distances and evaluate how the shape and power of a vehicle can be altered to increase the vehicle's top speed. The key points to remember about stopping distances are that they involve a thinking distance and a braking distance. Anything that slows down a person's thinking such as drugs and alcohol will increase the thinking distance - the car will have travelled further. If a car's brakes are worn or otherwise in a poor condition, or the tyres are worn, the braking system will not work as effectively, increasing the braking distance. You also need to know that adverse conditions that reduce the frictional force of the tyres on the road will also increase the braking distance. The key points to remember about increasing a vehicle's top speed are that air resistance, mass and driving force from the engine are all involved.

You will be expected to be able to draw and interpret velocity-time graphs for objects that reach terminal velocity, including a consideration of the forces acting on the object. The sort of thing that you may be asked to do is to sketch a graph showing the speed and velocity of a skydiver before and after they have opened their parachute. For cars, you may have to interpret the forces acting on the car based on a graph. You need to know how to work out acceleration and distance travelled from graphs too and there are a few simple equations that you need to learn.