Year 5 Science: Water resistance
Part of the Year 5 Science gravity, friction and resistance chapter. Chapter overview · whole chapter on one page
Water resistance
Water resistance is a force that acts against things moving through water. Like air resistance, it pushes against the motion and slows the object down.
A flat, blunt shape pushes a lot of water out of the way, so it has more water resistance. A streamlined shape, which is smooth and pointed, lets the water flow past it more easily, so it has less water resistance.
| Shape moved through water | Water resistance |
|---|---|
| a flat, blunt boat shape | more water resistance |
| a smooth, pointed boat shape | less water resistance |
Key ideas
- Water resistance is a force that slows down moving things in water.
- A flat, blunt shape has more water resistance than a streamlined shape.
- Streamlined shapes help things to move through water with less resistance.
- Water resistance acts against the motion.
Method. Read the table in section 9.3.
- Read the table. The flat, blunt shape has more water resistance.more water resistance
- Choose the shape. So the flat, blunt boat shape has more water resistance.a flat, blunt boat shape
- Write the answer. a flat, blunt boat shape
Check. The flat shape pushes more water out of the way. ✓
Method. Read the key ideas.
- Read the definition. Water resistance is a force that slows down moving things in water.slows down moving things
- Name the force. The name is water resistance.water resistance
- Write the answer. water resistance
Check. Water resistance acts against the motion. ✓
Method. Think about the streamlined shape.
- Think about the shape. A smooth, pointed shape lets water flow past it more easily.flow past
- Decide. So a streamlined shape helps it move through water, and the answer is yes.yes
- Write the answer. yes
Check. Streamlined shapes have less water resistance. ✓
Watch out
Watch out: water resistance and air resistance are both forces that push against the motion. They are not the same force, because one acts in air and the other acts in water.
Try it (with your teacher or a grown-up). With your teacher, use a tray of water and two small pieces of card of the same size. Move one flat, sideways, through the water, and the other edge first. Which one feels harder to move? Record your answer, and keep the water in the tray.
Exam tip
Grown-up tip. Ask: “Which one felt harder to push? Why do you think the flat one pushed more water?” Keep the tray on a table, away from the edge.
Exercise 9C Water resistance
Method. Read section 9.3.
- Read the definition. Water resistance is a force that slows down moving things in water.in water
- Name it. The name is water resistance.water resistance
- Write the answer. water resistance
Check. It acts against the motion. ✓
Method. Read the table in section 9.3.
- Read the table. The flat, blunt shape has more water resistance.more water resistance
- Choose the shape. So the flat, blunt shape has more water resistance.a flat, blunt shape
- Write the answer. a flat, blunt shape
Check. A flat shape pushes more water out of the way. ✓
Method. Read section 9.3.
- Read the description. A streamlined shape is smooth and pointed.smooth and pointed
- Choose the shape. So the smooth, pointed shape is streamlined.a smooth, pointed shape
- Write the answer. a smooth, pointed shape
Check. A streamlined shape lets water flow past it. ✓
Method. Read the key ideas in section 9.3.
- Read the key idea. Streamlined shapes have less water resistance.less water resistance
- Choose the word. So the answer is less.less
- Write the answer. less
Check. Streamlined shapes help things move through water. ✓
Method. Read the key ideas in section 9.3.
- Read the key idea. Water resistance acts against the motion.against the motion
- Fill the gap. So the missing word is motion.motion
- Write the answer. motion
Check. It pushes back against the way the object moves. ✓
Method. Think about the name of the force.
- Think about the name. Water resistance acts in water, and air resistance acts in air.in water
- Decide. So water resistance does not act in air, and the answer is no.no
- Write the answer. no
Check. The two forces act in different materials. ✓
Method. Read the arrows in the picture.
- Read the arrows. The orange arrow points to the left, against the motion.to the left
- Choose the word. So the water resistance arrow points to the left.left
- Write the answer. left
Check. The motion is to the right, so the resistance acts to the left. ✓
Method. Think about which shape has less water resistance.
- Think about the shapes. The pointed shape has less water resistance.less
- Decide. So Ruby is not right.no
- Write the answer. no
Check. A streamlined shape moves more easily through water. ✓
Method. Think about water resistance.
- Think about the shapes. The pointed card has less water resistance.less
- Make the prediction. So the pointed card should reach the far side first.pointed
- Write the answer. pointed
Check. Test your prediction with your teacher, in a tray. ✓
Method. Think about how the water moves.
- Think about the water. The water flows past a smooth, pointed shape more easily.flows past
- Write the reason. So the boat has less water resistance.less water resistance
- Write the answer. Accept any sentence that says a streamlined shape lets the water flow past it, so there is less water resistance.
Check. Less water resistance means the boat moves more easily. ✓
Method. Think about the water.
- Think about the shape. A smooth body lets water flow past.flow past
- Write the reason. So there is less water resistance, which helps it to move.less water resistance
- Write the answer. Accept any sentence that says a smooth shape reduces water resistance, so the body moves through water more easily.
Check. Streamlined shapes save energy when moving through water. ✓