Physics P1: Motion, Forces, Energy and Radioactivity

The physics of motion and matter

Physics P1 is about how things move, what makes them move, and where the energy goes. It brings together four big ideas. Motion describes how fast something travels and how quickly that changes. Forces are the pushes and pulls that start, stop or turn a moving object. Energy is the ability to make things happen, and one of the deepest rules in science is that energy is never lost, only moved from one form to another. Finally, radioactivity is the way some atoms break down over time, measured by their half-life. This module works through each of these, shows you how to find a speed, and links them together, so the P1 exam questions become a set of ideas you can reason about rather than facts to memorise.

P1 physics words

Learn these five terms before you reason about motion, forces and energy.

Match each physics quantity to its unit

Balanced against unbalanced forces

Whether the forces on an object are balanced decides whether its motion changes.

Where did the movement go?

A ball rolling along flat ground gradually slows and then stops. Where has its movement energy mainly gone?

• It has transferred to heat through friction
• It has been destroyed
• It has turned into extra mass
• It has simply vanished into nothing

Energy is never lost, only moved

One rule sits underneath the whole of P1: energy cannot be created or destroyed, only transferred from one form to another. When a car brakes, its movement energy does not disappear; it is carried away as heat in the brakes. When you lift a bag, the energy from your muscles is stored because of its raised position. If you add up the energy in every form before and after any event, the totals match. This is why physicists talk about energy being wasted rather than lost: the so-called wasted energy has usually spread out as heat, where it is hard to use again. When a question asks where energy went, the answer is never that it disappeared.

Pick the true physics facts

Select every statement about P1 physics that is true.

• Speed is how far something travels in a certain time
• Unbalanced forces change how an object moves
• Energy is never created or destroyed, only transferred
• A force is just another word for energy
• Radioactivity can be switched off with a switch

Order how to find a speed

Put the steps of working out a speed in the correct order.

• Measure the distance travelled
• Measure the time taken
• Divide the distance by the time
• Write the answer with its unit
• Check the answer is sensible

Complete the physics facts

How far something travels in a certain time is its _____. A push or a pull is a _____. The ability to make something happen is _____. The time for half the radioactive atoms in a sample to decay is the _____.

Money moving between pockets

Think of the money you carry. If you move ten pounds from your left pocket to your right, or out of a pocket and into the bank, the amount you own has not changed at all; it has only moved from one place to another. You could follow it as it shifts about, and the total would always add up to the same figure. Physics treats the ability to make things happen in the very same way. It is never made out of nothing and never simply disappears. It only moves from one form to another, and if some of it seems to go missing, it has usually slipped away quietly as heat. Add up every place it has ended up, and the total will always match the amount you started with.

Tap the forms of energy

Tap every item below that is a genuine store or form of energy.

• movement energy
• heat energy
• energy stored in a stretched spring
• the colour of the object

Work out the average speed

A runner covers 100 metres in 20 seconds. Speed is the distance divided by the time. What is the average speed in metres per second?

Reason about the physics

Read each situation and choose the best answer.

• A parachutist falls at a steady speed, neither speeding up nor slowing down. What does this tell you about the forces on them?
• A radioactive sample has a half-life of two days. After two days, how much of the original radioactive atoms remain?
• A moving car brakes and comes to a stop. What has happened to its movement energy?

Build a P1 physics point

Choose the word for each gap to complete one accurate point about P1 physics.

Explain the core ideas of P1 physics

A friend finds physics confusing and asks you to explain the big ideas of motion, forces and energy. Explain them clearly.

• Explain what speed and acceleration are
• Explain the difference between balanced and unbalanced forces
• Explain how to work out a speed
• Explain what conservation of energy means
• Explain what radioactivity and half-life are