Year 5 Science: Air resistance
Part of the Year 5 Science gravity, friction and resistance chapter. Chapter overview · whole chapter on one page
Air resistance
Air resistance is a force that acts against things moving through air. It pushes against the motion, so it slows the thing down.
A larger flat surface catches more air, so it has more air resistance. A small, streamlined shape has less air resistance, and it falls faster.
The table shows the results of a fair test. Each parachute was dropped from the same height, three times, and the time to reach the floor was measured.
| Parachute area (cm²) | Trial 1 (tenths of a second) | Trial 2 | Trial 3 | Mean (tenths of a second) |
|---|---|---|---|---|
| 100 | 8 | 7 | 9 | 8 |
| 200 | 10 | 11 | 9 | 10 |
| 300 | 12 | 11 | 13 | 12 |
| 400 | 16 | 15 | 17 | 16 |
Key ideas
- Air resistance is a force that slows down moving things in air.
- Air resistance acts against the motion of a falling object.
- A larger flat surface has more air resistance, and falls more slowly.
- A fair test changes only the area of the parachute, and keeps everything else the same.
Method. Read the mean for 200 cm².
- Read the row. The 200 cm² row has a mean of 10 tenths of a second.10 tenths
- Write in seconds. Ten tenths of a second is 1.0 second.1.0
- Write the answer. 1.0
Check. Check: 10 tenths = 1.0 second. ✓
Watch out. Tenths of a second: 10 tenths is 1.0 second.
Method. Find the longest mean time.
- Compare the means. The 100 cm² parachute has a mean of 8 tenths, and the 400 cm² one has 16 tenths.8 and 16
- Choose the slower. The longer time is 16 tenths, so the 400 cm² parachute falls more slowly.400 cm²
- Write the answer. 400 cm²
Check. Larger parachutes fall more slowly in this test. ✓
Method. Subtract the smaller time from the larger.
- Read the two means. The 400 cm² mean is 16 tenths, and the 100 cm² mean is 8 tenths.16 and 8
- Subtract. The difference is 16 minus 8, which is 8 tenths.16 - 8 = 8
- Write the answer. 8
Check. Check: 8 + 8 = 16. ✓
Watch out
Watch out: the parachute with more air resistance falls more slowly. A heavier object is not what makes it fall faster; here the wider one is the slower one.
Try it (with your teacher or a grown-up). Take two sheets of the same paper. Drop one flat and the other crumpled into a tight ball, from the same height onto a rug. Time each fall three times, and find the mean. Which shape had more air resistance? Stand on the floor, not on a chair.
Exam tip
Grown-up tip. Ask: “Which shape catches more air? Which falls more slowly?” Let your child find the mean of three times.
Exercise 9B Air resistance
Method. Read section 9.2.
- Read the definition. Air resistance is a force that slows down moving things in air.slows down
- Name it. The name is air resistance.air resistance
- Write the answer. air resistance
Check. Air resistance pushes against the motion. ✓
Method. Read the key ideas in section 9.2.
- Read the key idea. A larger flat surface catches more air.catches more air
- Choose the surface. So the large flat surface has more air resistance.a large flat surface
- Write the answer. a large flat surface
Check. More air caught means more air resistance. ✓
| Parachute area (cm²) | Trial 1 (tenths of a second) | Trial 2 | Trial 3 | Mean (tenths of a second) |
|---|---|---|---|---|
| 100 | 8 | 7 | 9 | 8 |
| 200 | 10 | 11 | 9 | 10 |
| 300 | 12 | 11 | 13 | 12 |
| 400 | 16 | 15 | 17 | 16 |
Method. Read the row for 300 cm².
- Read the row. The 300 cm² row has a mean of 12 tenths of a second.12
- Write the number. So the mean is 12 tenths.12
- Write the answer. 12
Check. 12 tenths of a second is 1.2 seconds. ✓
| Parachute area (cm²) | Trial 1 (tenths of a second) | Trial 2 | Trial 3 | Mean (tenths of a second) |
|---|---|---|---|---|
| 100 | 8 | 7 | 9 | 8 |
| 200 | 10 | 11 | 9 | 10 |
| 300 | 12 | 11 | 13 | 12 |
| 400 | 16 | 15 | 17 | 16 |
Method. Read the row for 100 cm².
- Read the row. The 100 cm² row has trial 2 as 7 tenths.7
- Write the number. So trial 2 was 7 tenths.7
- Write the answer. 7
Check. Trial 2 is the second number in the row. ✓
| Parachute area (cm²) | Trial 1 (tenths of a second) | Trial 2 | Trial 3 | Mean (tenths of a second) |
|---|---|---|---|---|
| 100 | 8 | 7 | 9 | 8 |
| 200 | 10 | 11 | 9 | 10 |
| 300 | 12 | 11 | 13 | 12 |
| 400 | 16 | 15 | 17 | 16 |
Method. Add the three trials, then divide by three.
- Add the trials. The three trials are 16, 15 and 17, which add to 48.16 + 15 + 17 = 48
- Divide by three. Divide 48 by 3 to get the mean.48 divided by 3 is 16
- Write the answer. 16
Check. Check: 16 + 16 + 16 = 48. ✓
| Parachute area (cm²) | Trial 1 (tenths of a second) | Trial 2 | Trial 3 | Mean (tenths of a second) |
|---|---|---|---|---|
| 100 | 8 | 7 | 9 | 8 |
| 200 | 10 | 11 | 9 | 10 |
| 300 | 12 | 11 | 13 | 12 |
| 400 | 16 | 15 | 17 | 16 |
Method. Find the shortest mean time.
- Find the shortest. The shortest mean time is 8 tenths, for the 100 cm² parachute.8 tenths
- Name the area. So the parachute that falls fastest is 100 cm².100
- Write the answer. 100 cm²
Check. A smaller parachute falls faster in this test. ✓
Method. Compare the two bars.
- Compare the bars. The 300 cm² bar shows 1.2 seconds, and the 200 cm² bar shows 1.0 second.1.2 and 1.0
- Choose the word. So the 300 cm² bar is taller.taller
- Write the answer. taller
Check. Larger parachutes fall more slowly. ✓
Method. Read the key ideas in section 9.2.
- Read the key idea. A larger flat surface has more air resistance.more air resistance
- Decide. So the statement is true.true
- Write the answer. true
Check. The larger parachute catches more air. ✓
Method. Think about the air each parachute catches.
- Think about the large parachute. The large parachute catches more air.catches more air
- Write the reason. So it has more air resistance, and falls more slowly.falls more slowly
- Write the answer. Accept any sentence that says the large parachute catches more air, so it has more air resistance.
Check. Air resistance pushes up against the falling parachute. ✓
Method. Think about what makes a fair test.
- Think about the test. Only the area should change between parachutes.only the area
- Write one thing. The height, the release and the material must stay the same.stay the same
- Write the answer. Accept any one of: the same height, the same release, the same material.
Check. A fair test changes only one thing. ✓
Method. Think about repeats.
- Think about repeats. Repeat trials show whether the results agree.agree
- Write the reason. So the mean of the trials is more reliable.more reliable
- Write the answer. Accept any sentence that says repeats show whether the results agree, and the mean is more reliable.
Check. Three trials give a more reliable mean. ✓