Year 5 Science: Choosing a mechanism for a job
Part of the Year 5 Science levers, pulleys and gears chapter. Chapter overview · whole chapter on one page
Choosing a mechanism for a job
Every mechanism uses a smaller force to have a greater effect, in a different way:
| Object | Mechanism used | What the smaller force does |
|---|---|---|
| a seesaw | lever | a light child can lift a heavy child on the far end |
| a wheelbarrow | lever | a smaller push lifts a heavier load |
| a bicycle, with a small gear at the front and a large gear at the back | gears | the pedals turn the wheel with more force, though more slowly |
| a crane lifting a heavy load on a rope | pulley | a movable pulley shares the load between two ropes |
Key ideas
- A lever uses a long arm, so that a small effort can lift a load.
- A movable pulley shares the load, so the effort is about half.
- Gears with different numbers of teeth change the speed and effect of turning.
- Choose the mechanism that fits the job, and give a reason.
Method. Read the row for the wheelbarrow.
- Read the row. The wheelbarrow row says lever.lever
- Name the mechanism. So the mechanism is a lever.lever
- Write the answer. lever
Check. A wheelbarrow works like a lever on its wheel. ✓
Method. Read the row for the bicycle.
- Read the row. The bicycle row says gears.gears
- Name the mechanism. So the mechanism is gears.gears
- Write the answer. gears
Check. The bicycle’s gears change the effect of the pedals. ✓
Method. Think about which mechanism shares the load.
- Think about the rope. A movable pulley shares the load between two parts of the rope.shares the load
- Name the mechanism. So the best mechanism is a pulley.pulley
- Write the answer. pulley
Check. A movable pulley halves the effort needed. ✓
Watch out
Watch out: a mechanism does not make the work disappear. A lever, a pulley or gears can make the effort smaller, but it often has to move further.
Try it (with your teacher or a grown-up). Make a lever with a ruler and a pencil, and a second lever with a longer ruler. With your teacher, use the same small weight to lift the same load on each. Which lever did it more easily? Write one sentence giving your reason.
Exam tip
Grown-up tip. Ask: “Which machine did the job more easily? Why do you think so?” Let your child give a reason based on what they saw.
Exercise 10D Choosing a mechanism for a job
| Object | Mechanism used | What the smaller force does |
|---|---|---|
| a seesaw | lever | a light child can lift a heavy child on the far end |
| a wheelbarrow | lever | a smaller push lifts a heavier load |
| a bicycle, with a small gear at the front and a large gear at the back | gears | the pedals turn the wheel with more force, though more slowly |
| a crane lifting a heavy load on a rope | pulley | a movable pulley shares the load between two ropes |
Method. Read the mechanism column.
- Read the column. The seesaw row says lever.lever
- Name the object. So the object is a seesaw, and a wheelbarrow also uses a lever.a seesaw
- Write the answer. a seesaw
Check. A seesaw is a simple lever. ✓
| Object | Mechanism used | What the smaller force does |
|---|---|---|
| a seesaw | lever | a light child can lift a heavy child on the far end |
| a wheelbarrow | lever | a smaller push lifts a heavier load |
| a bicycle, with a small gear at the front and a large gear at the back | gears | the pedals turn the wheel with more force, though more slowly |
| a crane lifting a heavy load on a rope | pulley | a movable pulley shares the load between two ropes |
Method. Read the mechanism column.
- Read the column. The crane row says pulley.pulley
- Name the object. So the object is a crane lifting a load on a rope.a crane
- Write the answer. a crane lifting a heavy load on a rope
Check. A crane uses pulleys to lift loads. ✓
| Object | Mechanism used | What the smaller force does |
|---|---|---|
| a seesaw | lever | a light child can lift a heavy child on the far end |
| a wheelbarrow | lever | a smaller push lifts a heavier load |
| a bicycle, with a small gear at the front and a large gear at the back | gears | the pedals turn the wheel with more force, though more slowly |
| a crane lifting a heavy load on a rope | pulley | a movable pulley shares the load between two ropes |
Method. Read the bicycle row.
- Read the row. The bicycle row says gears.gears
- Name it. So the mechanism is gears.gears
- Write the answer. gears
Check. The bicycle uses gears to make pedalling easier. ✓
| Object | Mechanism used | What the smaller force does |
|---|---|---|
| a seesaw | lever | a light child can lift a heavy child on the far end |
| a wheelbarrow | lever | a smaller push lifts a heavier load |
| a bicycle, with a small gear at the front and a large gear at the back | gears | the pedals turn the wheel with more force, though more slowly |
| a crane lifting a heavy load on a rope | pulley | a movable pulley shares the load between two ropes |
Method. Read the seesaw row.
- Read the row. A light child can lift a heavy child on the far end.light child
- Name the effect. So the smaller force lifts a heavier child.lifts a heavier child
- Write the answer. lifts a heavier child
Check. The longer arm helps the light child. ✓
Method. Think about which mechanism shares the load.
- Think about the rope. A movable pulley shares the load between two ropes.two ropes
- Choose the mechanism. So a pulley is the best choice.pulley
- Write the answer. pulley
Check. A movable pulley halves the effort. ✓
Method. Think about the bicycle.
- Think about the bicycle. A small gear at the back makes the pedals easier to turn.easier to turn
- Choose the mechanism. So gears are the best choice.gears
- Write the answer. gears
Check. Gears change the effect of the pedals. ✓
Method. Think about the handle.
- Think about the handle. A long handle gives a long effort arm, which makes the effort easier.long handle
- Choose the mechanism. So a lever is the best choice.lever
- Write the answer. lever
Check. A longer arm makes the effort easier. ✓
Method. Think about the effort arm.
- Think about the handle. A long handle gives a long effort arm.long handle
- Write the reason. So a smaller effort turns the lid, which is easier.easier
- Write the answer. Accept any sentence that says a longer effort arm, such as a long handle, makes the effort smaller, so the lid is easier to turn.
Check. A longer effort arm makes the effort easier. ✓
Method. Think about the evidence in the table.
- Think about the table. A movable pulley needs 4 weights, and no pulley needs 8.4 and 8
- Write the reason. So the movable pulley needs about half the effort.about half
- Write the answer. Accept any sentence that says the load is shared, so the effort needed is about half.
Check. The evidence from the table supports the choice. ✓
Method. Think about what pulleys do.
- Think about the crane. A crane lifts very heavy loads.heavy loads
- Write the reason. Pulleys make the lift easier, by sharing the load or changing the direction.changing the direction
- Write the answer. Accept any sentence that says pulleys can make lifting easier, by sharing the load or changing the direction of the pull.
Check. Pulleys help lift heavy loads with less effort. ✓