Year 5 science · Key Stage 2 · Forces
Year 5 forces: gravity, resistance and simple machines
In Year 5, children find out that unsupported objects fall because of gravity, which pulls between the Earth and the object. They also learn about forces that act between moving surfaces: air resistance, water resistance and friction. Finally, they meet levers, pulleys and gears, which are simple machines that let a small force have a bigger effect.
Gravity, resistance and simple machines, explained
A force is a push or a pull, and forces are measured in newtons using a force meter. Children first meet pushes, pulls and magnets in Year 3, and in Year 5 they get a name for the pull that makes things fall. Gravity is a force that pulls objects towards each other. Because the Earth is so large, its pull is the one we notice: an apple drops from a branch, a ball thrown up comes back down, and we stay on the ground. Gravity acts between the Earth and the falling object, and the object pulls on the Earth too, although the Earth is far too big for us to see it move. Some schools choose to look at how Galileo Galilei and Isaac Newton helped to develop the theory of gravitation.
Some forces act when surfaces move against each other or through something. Air resistance is the push of air against something moving through it, and water resistance is the same in water. Both slow the object down. Friction is the force between two surfaces that rub together. It slows or stops movement and makes the surfaces warm. Friction is not always unwelcome: brakes, shoe grips and bike tyres depend on it, while oil on a bicycle chain is there to reduce it. Streamlined shapes, such as a pointed boat or a cyclist crouching low, have less air or water resistance.
Resistance explains the way things fall. A sheet of paper flutters down but the same sheet, screwed into a ball, falls quickly. Gravity pulls on both, but the flat sheet has a larger area for the air to push against. A parachute works because its large canopy catches a lot of air, so the upward air resistance is big and the fall is slower. A sycamore seed spins as it falls for a similar reason, which gives the wind longer to carry it away from the parent tree.
The last idea is that some mechanisms let a smaller force have a greater effect. A lever, like a seesaw or a crowbar, turns around a fixed point called the pivot, and pushing on the long end gives a bigger force at the short end. A pulley is a wheel with a rope over it; one pulley changes the direction of a pull, and a system of several pulleys makes a heavy load easier to lift. Gears are toothed wheels that mesh together, and the sizes of the wheels change how fast and how forcefully they turn. Bicycle gears are the familiar example. The trade-off is that you push or pull over a longer distance. Children aren’t expected to explain why, only to recognise these examples and describe what they do.
Words your child will hear
- Gravity
- The force that pulls objects towards each other. On Earth it pulls everything towards the ground.
- Air resistance
- The force of air pushing against something moving through it, which slows it down.
- Water resistance
- The force of water pushing against something moving through it.
- Friction
- The force between surfaces that rub together, which slows or stops movement.
- Streamlined
- Shaped to let air or water flow past easily, so there is less resistance.
- Newton (N)
- The unit used to measure forces. A force meter shows forces in newtons.
- Pivot
- The fixed point a lever turns around, such as the middle of a seesaw.
What the National Curriculum says
In Year 5, pupils should be taught to:
- Explain that unsupported objects fall towards the Earth because of the force of gravity acting between the Earth and the falling object
- Identify the effects of air resistance, water resistance and friction, that act between moving surfaces
- Recognise that some mechanisms, including levers, pulleys and gears, allow a smaller force to have a greater effect
Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.
Try it: planning a fair test with a parachute
Does the size of a parachute change how long it takes to fall?
- Predict and explain. “I think a bigger parachute will fall more slowly, because it has more area for the air to push on, so there is more air resistance.”
- Choose what to change: the size of the square canopy, such as 20 cm, 30 cm and 40 cm sides. Choose what to measure: the time to fall, in seconds.
- Keep everything else the same. Use the same material for each canopy, the same string length, the same weight hanging underneath (for example a lump of modelling clay of the same size) and the same drop height each time. Let go rather than throwing.
- Take readings and repeat. Time each parachute three times to spot odd results, and record them in a table. Example results for the 30 cm parachute: 1.5 s, 1.7 s and 1.6 s, which average 1.6 s.
- Look for the pattern. If the average times are about 1.1 s for 20 cm, 1.6 s for 30 cm and 2.1 s for 40 cm, the bigger parachutes fell more slowly. Say why: bigger canopies catch more air, so more air resistance acts against gravity.
The larger the parachute canopy, the more slowly it falls, because a larger canopy produces more air resistance pushing up against gravity. The numbers here are only examples: in a real test your child uses their own repeated measurements to decide.
Common mistakes and how to help
Thinking heavier things always fall faster
A hammer falls faster than a feather in everyday life, so children assume weight is the cause.
What helps: Drop a flat sheet of paper and a scrunched one together. The same material falls differently, so shape and air resistance matter, not just weight.
Believing there is no gravity in the air, in space or on the Moon
Pictures of astronauts floating suggest gravity has been switched off.
What helps: Explain that gravity acts everywhere, getting weaker with distance. The Moon has its own, weaker pull, and astronauts float because they are in free fall.
Seeing friction and air resistance as always bad
Children notice them as things that slow a scooter or bike down.
What helps: Ask what would happen with no friction between shoes and floor, or between bike brakes and wheels. Sort examples into helpful and unhelpful.
Thinking a lever or pulley gives you free strength
It feels as if the machine is doing the work, because the push needed is so much smaller.
What helps: Notice that you move the end of the lever or pull the rope much further. A smaller force over a longer distance gets the same job done.
How to help at home
- Paper drop test. Drop a flat sheet and a scrunched-up sheet from the same height at the same time, then try a folded sheet. Ask your child to explain the order they land, using the words gravity and air resistance.
- Make a parachute. Make canopies from a carrier bag or a square of cloth, string and a small weight such as a metal washer or modelling clay. Test the effect of size by dropping each from the same height and timing the fall with a stopwatch or a phone timer. Standing on the floor with an arm stretched high is enough height. Never drop them out of a window or over a stair banister.
- Friction hunt. Slide a toy car down the same ramp covered with carpet, a tea towel, wood and foil. Predict the order first and discuss which surface has the most friction.
- Water resistance race. Fill a tall clear jug or plastic bottle with water. Shape three equal lumps of modelling clay into a ball, a flat pancake and a pointed torpedo, drop each in and watch which reaches the bottom first. Ask your child which shape has the least water resistance and why.
- Lever and pulley play. Lift a book with a ruler as a lever over a pencil as a pivot, then move the pivot closer to the book and see what changes. Try a toy pulley, or a loop of string over a smooth rail, to see the direction of the pull change. A bicycle’s gears give a real-life example, with an adult nearby.
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