IGCSE Physics / Forces and shape
What forces do and the types of force
Edexcel International GCSE Physics (4PH1), chapter 2: Forces and shape, specification point 1.11, 1.12. Free lesson.
Read the revision notes · IGCSE Physics past papers
A force is a push or pull between two objects, measured in newtons (N). Forces can change an object's motion or shape, and are classified as contact or non-contact forces.
What a force is and what it can change
A force is a push or a pull that one object exerts on another. It is measured in newtons (N). When describing a force, name both objects, such as the hand pushing the door or the Earth pulling the ball. A force can change an object's motion or its shape. Speed: a force can make an object speed up or slow down, such as a kick starting a ball or brakes slowing a bike. Direction: a force can make an object move in a different direction, such as a bat sending a ball back. Shape: a force can squash, stretch, bend or twist an object, such as a spring or sponge. One force can…
How to recognise contact forces
Contact forces act only while the objects are touching. Learn their exact names, because questions may ask you to identify them. Friction acts between touching surfaces and opposes motion, such as a box sliding across a floor. Drag acts on an object moving through a fluid, meaning a gas or liquid. It is called air resistance in air and water resistance in water. Tension is the pull in a stretched rope, string or cable, such as a lift cable. Normal reaction is the push from a surface. Normal means at right angles to the surface, so a table pushes upwards on a book.…
How to recognise non-contact forces
Non-contact forces act across a gap, so the objects do not have to touch. Each force still acts between two objects. Gravitational force pulls any two masses towards each other. The Earth's pull on you is your weight. Electrostatic force acts between electric charges. A rubbed balloon can attract pieces of paper without touching them. Magnetic force acts between magnets, or between a magnet and iron. A magnet can pull a paperclip across a gap.
How to label forces on a book
A force diagram shows the forces acting on an object. For a book resting on a table, the Earth's gravitational pull acts downwards as the book's weight. The table pushes upwards with a normal reaction. Both forces are 5 N, so their arrows have equal lengths. Draw one ruled arrow for each force. Each arrow starts on the object and its length matches the force's size. Label the downward force as weight, not gravity. Gravity is the cause; the force on the object is called its weight.
State effects of a force
When asked what a force does to an object, use the three possible effects: a change in speed, direction or shape. Give the number of different effects the question asks for. For a footballer kicking a moving ball that flies off in a new direction, possible effects include a change in direction, a change in speed, and a change in shape while the foot touches it.