Forces
KS2SC-KS2-D013
Physics domain covering gravity, air resistance, water resistance, friction, and mechanisms (levers, pulleys, gears). Year 5 only. Builds on Y3 forces and magnets work on contact/non-contact forces.
National Curriculum context
Forces at upper KS2 moves beyond the qualitative introduction of Year 3 to a more quantitative understanding, including gravity, air resistance, water resistance and mechanisms that can change the effect of forces. Pupils investigate how objects fall due to gravity and explore the effects of air resistance and water resistance in opposing motion. The statutory curriculum requires pupils to understand that some mechanisms — levers, pulleys and gears — allow a smaller force to have a greater effect, introducing the concept of mechanical advantage. Pupils design and evaluate fair tests investigating factors that affect the force of air resistance or water resistance, developing their scientific investigation skills.
3
Concepts
2
Clusters
2
Prerequisites
3
With difficulty levels
Lesson Clusters
Explain how gravity and resistance forces affect motion
introduction CuratedGravity and resistance forces (air resistance, water resistance, friction) are co-taught (co_teach_hints link C055 and C056) because they act in opposition: gravity pulls objects down while resistance slows their fall.
Investigate how levers, pulleys and gears act as force multipliers
practice CuratedMechanisms as force multipliers is a distinct practical investigation cluster at KS2 that applies force understanding to simple machines; it introduces the efficiency trade-off concept that continues at KS3.
Prerequisites
Concepts from other domains that pupils should know before this domain.
Concepts (3)
Gravity
knowledge AI DirectSC-KS2-C055
Understanding that gravity is a non-contact force of attraction acting between the Earth and objects. Unsupported objects fall towards Earth because of gravity. Gravity is responsible for keeping planets in orbit around the Sun and the Moon in orbit around Earth.
Teaching guidance
Drop a range of objects (feather, ball, piece of paper, stone) and observe that unsupported objects fall due to gravity. Discuss why a feather falls more slowly than a ball — air resistance, not less gravity. Use the term 'gravitational force' or 'gravitational pull' and explain it as an attractive force between the Earth and all objects. Demonstrate that gravity acts on all objects regardless of mass by dropping two objects of different mass but similar shape from the same height. Discuss gravity's role in keeping planets orbiting the Sun and the Moon orbiting Earth. Connect to the concept of weight as a measure of gravitational force.
Common misconceptions
Children commonly believe heavier objects fall faster than lighter ones. In a vacuum they fall at the same rate — in air, differences are caused by air resistance, not gravity. Some pupils think gravity only exists on Earth or only works at the Earth's surface. Children may confuse mass and weight — mass is the amount of matter (measured in kg), weight is the gravitational force acting on that mass (measured in Newtons). Some pupils think there is no gravity in space.
Difficulty levels
Knowing that things fall down when you let go of them, and that this is because of gravity.
Example task
What happens when you drop a ball? Why does it fall down and not up?
Model response: The ball falls down to the ground. It falls because of gravity. Gravity is a force that pulls everything down towards the Earth.
Understanding that gravity is a pulling force that acts between the Earth and all objects, and that it works without physical contact (non-contact force).
Example task
How is gravity different from pushing something? You do not have to touch the ball to make it fall.
Model response: When you push something, your hand touches it — that is a contact force. But gravity pulls the ball down without anything touching it — the Earth pulls the ball through empty space. That makes gravity a non-contact force, like magnetism. Gravity acts on everything — heavy objects, light objects, you, the air, water. Everything on Earth is being pulled towards the ground by gravity all the time.
Explaining that gravity acts on all objects regardless of mass, and distinguishing between the effect of gravity and air resistance when objects fall at different rates.
Example task
A stone and a feather are dropped at the same time. The stone hits the ground first. Does gravity pull harder on the stone?
Model response: Gravity pulls on both objects. The feather falls more slowly not because gravity is weaker, but because air resistance has a greater effect on the feather. The feather has a large surface area relative to its weight, so air pushes against it more effectively, slowing it down. In a vacuum (no air), they would fall at exactly the same rate — this was demonstrated on the Moon by Apollo 15 astronaut David Scott, who dropped a hammer and a feather and they hit the ground together. The difference we see in everyday life is caused by air resistance, not by different amounts of gravity.
Explaining gravity's role in the solar system — keeping planets in orbit around the Sun and moons in orbit around planets — and understanding that gravity acts between all objects with mass.
Example task
What stops the Moon from flying off into space? What stops it from crashing into Earth?
Model response: The Moon is constantly being pulled towards Earth by gravity — this pull stops it flying off into space. But the Moon is also moving sideways at just the right speed. The combination of gravity pulling inward and the Moon's sideways motion means it continuously falls towards Earth but keeps missing — this curved path is an orbit. If the Moon were slower, it would spiral in. If faster, it would fly away. The same principle keeps planets orbiting the Sun and satellites orbiting Earth. Gravity is the force that holds the entire solar system together. It acts between all objects with mass — the Earth pulls the Moon, and the Moon pulls the Earth (causing tides). Even you and your desk pull on each other with gravity, but the force is far too weak to notice because your masses are so small compared to the Earth.
Delivery rationale
Science knowledge concept — factual content deliverable with visual representations and adaptive quizzing.
Resistance Forces
knowledge AI DirectSC-KS2-C056
Understanding that air resistance, water resistance and friction are forces that act against motion between moving surfaces. These forces slow objects down and can be useful (parachutes, brakes) or a problem (inefficiency). Friction acts between surfaces in contact.
Teaching guidance
Investigate air resistance by dropping paper shapes of different sizes and observing fall rates. Design and test parachutes of different sizes and materials, measuring the time they take to fall a fixed distance. Investigate water resistance by pulling different shapes through water and comparing the force required. Compare friction on different surfaces using a force meter to pull a shoe across carpet, wood, tile and sandpaper. Discuss the design features of real objects that minimise resistance (streamlined cars, cyclists' clothing) or maximise it (parachutes, brake pads, non-slip shoes). Link to fair testing — changing one variable at a time.
Common misconceptions
Children often think that moving objects have a force pushing them forward even after the push has stopped. Once no force acts, the object slows due to friction and air resistance. Some pupils believe friction only acts when objects are moving — static friction also acts to prevent objects from starting to move. Children may think that air resistance only affects large objects like parachutes, not recognising it acts on all moving objects.
Difficulty levels
Knowing that some things slow you down — it is harder to run through water than through air, and rough surfaces slow you down more than smooth ones.
Example task
Is it easier to slide across a smooth floor or across carpet? Why?
Model response: It is easier to slide across a smooth floor. Carpet is rough and it slows you down more. The roughness creates a force that rubs against you.
Naming air resistance, water resistance and friction as forces that oppose motion, and giving examples of each.
Example task
Name three forces that slow objects down and give an example of each.
Model response: 1. Friction — when you slide a book across a desk, friction between the book and desk surface slows it down. 2. Air resistance — a parachute opens and air resistance slows the person's fall. 3. Water resistance — swimming is harder than walking because water pushes against you as you move through it. All three are contact forces that act against the direction of movement.
Investigating factors that affect resistance forces and explaining how these forces are used practically, including designing investigations.
Example task
Design a fair test to investigate how the size of a parachute affects the time it takes to fall. What results do you predict?
Model response: I will make parachutes of 3 different sizes (20cm, 40cm, 60cm across) using the same material (plastic bag) and attach the same weight to each. I will drop each from the same height (2 metres) and time how long it takes to reach the ground. I will keep the same: weight, material, drop height, and method of release. I predict the largest parachute will take the longest to fall because it has the biggest surface area, which catches more air and creates more air resistance. I will repeat each test 3 times and calculate the mean for reliability. This is why real parachutes are very large — more surface area means more air resistance and a slower, safer descent.
Explaining how resistance forces are both useful and problematic in real-world engineering, and understanding the concept of streamlining.
Example task
Cars, fish, aeroplanes and submarines all have similar streamlined shapes. Explain why, using your knowledge of resistance forces.
Model response: All four move through a fluid (air or water) and experience resistance that opposes their motion. A streamlined shape — pointed at the front, smooth, tapering at the back — allows the fluid to flow smoothly around the object rather than pushing against a flat surface. This reduces resistance and allows faster, more efficient movement. A flat-fronted bus uses more fuel than a streamlined car at the same speed because it has to push against more air resistance. Fish evolved streamlined bodies over millions of years because individuals with less water resistance could swim faster (escape predators, catch food). Engineers copied this principle from nature — called biomimicry. The trade-off is that streamlined shapes are harder to manufacture and offer less internal space than boxy designs. This is why lorries (prioritising cargo space) are less streamlined than sports cars (prioritising speed).
Delivery rationale
Science knowledge concept — factual content deliverable with visual representations and adaptive quizzing.
Mechanisms as Force Multipliers
knowledge AI FacilitatedSC-KS2-C057
Understanding that simple mechanisms — levers, pulleys and gears — allow a smaller input force to have a greater effect. These machines do not create energy but redistribute force and distance. Applications in everyday tools and machines.
Teaching guidance
Investigate levers by using a ruler balanced on a pencil to lift objects — explore how moving the fulcrum changes the effort needed. Explore pulleys using a simple pulley system to lift a weight — compare the force needed with and without the pulley. Examine gears using construction kits (LEGO Technic, K'Nex) to see how different-sized gears change speed and force. Identify mechanisms in everyday objects: scissors (lever), bicycle gears, fishing rod (lever), flagpole (pulley), clock mechanism (gears). Emphasise that these mechanisms do not create energy — they trade force for distance. A small force over a large distance can move a large load a small distance.
Common misconceptions
Children often think that machines create energy or force from nothing — they actually redistribute force and distance. A lever does not reduce the total work done; it allows a smaller force to be applied over a larger distance. Some pupils think pulleys only change the direction of force, not recognising that pulley systems with multiple wheels also provide mechanical advantage. Children may not recognise everyday objects (scissors, wheelbarrows, bottle openers) as levers.
Difficulty levels
Knowing that some tools make it easier to lift or move heavy things — for example, a see-saw, a wheelbarrow, or a ramp.
Example task
Which is easier: lifting a heavy box straight up, or pushing it up a ramp? Try both.
Model response: Pushing it up the ramp is easier. The ramp lets me use less force because I push over a longer distance.
Understanding that levers, pulleys and gears are simple mechanisms that allow a smaller force to have a greater effect, and identifying examples in everyday life.
Example task
How does a lever help you lift something heavy? Give an everyday example.
Model response: A lever is a rigid bar that pivots on a fixed point (fulcrum). When you push down on the long end, the short end lifts with more force than you applied. A crowbar is a lever — you push the long handle and the short end lifts a heavy nail. A see-saw is also a lever. A wheelbarrow uses the wheel as a fulcrum and the long handles let you lift a heavy load in the bucket.
Investigating how levers, pulleys and gears work, understanding that they trade force for distance, and explaining the effect of changing the position of the fulcrum.
Example task
You are trying to prize open a paint tin lid. Where should you place the fulcrum (the rim of the tin) relative to the lid — close to the lid or far from the lid? Explain using your knowledge of levers.
Model response: Place the fulcrum (rim) close to the lid you are trying to lift. This makes the effort arm (where you push) long and the load arm (where the lid is) short. A longer effort arm means less force is needed to lift the lid. If the fulcrum were far from the lid, you would have a short effort arm and would need much more force. This is the same principle as a see-saw: a heavy child can be lifted by a lighter child if the heavy child sits close to the pivot and the lighter child sits far from it. In all mechanisms, you trade distance for force — less effort but more movement.
Explaining that mechanisms do not create energy — they redistribute force and distance — and combining mechanisms to solve engineering problems.
Example task
A bicycle uses gears, levers and pulleys (chain on sprockets). How do these mechanisms work together to make cycling efficient?
Model response: The pedals and cranks are levers — your feet push on a long crank arm, which turns the front sprocket with less force but more effectively. The chain and sprockets are a pulley system — transferring force from the front cog to the rear cog. The gears allow you to change the ratio — a small front cog with a large rear cog gives less speed but more force (good for hills); a large front cog with a small rear cog gives more speed but needs more force (good for flat roads). Crucially, none of these mechanisms create energy. They redistribute the force your legs produce. Low gear: less force per pedal push but more pushes needed. High gear: more force needed per push but fewer pushes. The total work (energy) is the same — the mechanisms simply let you choose how to apply your effort. This is why 'perpetual motion machines' are impossible — mechanisms cannot produce more energy than you put in.
Delivery rationale
Science concept with significant practical requirements — AI delivers theory, facilitator manages practical.