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Falling and gravity About 400 years ago, Caltleo noticed that objects speed up, or accelerate, as they fall.
He found that heavy and light things, of the same shape and size, take the same time to fall to the ground. Gravity pulls then-* down equally.
Try this for yourself with different objects, like a slipper : and a heavy boot.
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Air resistance Objects of different shapes and sizes fall at different rates. The shape of a parachute makes people fall more slowly.
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| The air pushing against the parachute causes a lot of air resistance*. A person without a parachute falls faster because less air pushes against them. |
The faster something falls, the more air resistance there is on it. Eventually, the air resistance slowing it down becomes as strong as the pull of gravity. Then its speed no longer changes. This is called terminal speed. |
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Free fall If there were no air, there would be no air resistance. All falling objects would just get faster and faster < called is This rate. same the> free fall. | |
67. Falling objects are pulled down to the ground by .
A. gravity B. resistance C. speed D. acceleration（加速度）
68. Why do people make parachutes（降落伞）?
A. To look pretty and colourful in the air. B. To slow down the falling speed.
C. To push against the air in the sky. D. To accelerate the falling movement.
69. Which did Galileo discover?
A. A heavy ball falls faster than a light ball. B. A light ball falls faster than a heavy ball.
C. A light ball and a heavy ball fall at the same speed
D. A light ball and a heavy ball fall at different speed.
70. Which of the following is NOT true according to the passage？
A. Heavy and light objects fall equally when they are different in size.
B. When air resistance equals gravity, objects fall at terminal speed.
C. Without air; all falling objects get faster and faster at the same rate.
D. Slippers（拖鞋） and boots （靴子）fall at the same speed because they have the same shape
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Falling and gravity About 400 years ago, Caltleo noticed that objects speed up, or accelerate, as they fall.
He found that heavy and light things, of the same shape and size, take the same time to fall to the ground. Gravity pulls then-* down equally.
Try this for yourself with different objects, like a slipper : and a heavy boot.
|
|
Air resistance Objects of different shapes and sizes fall at different rates. The shape of a parachute makes people fall more slowly.
|
|
| The air pushing against the parachute causes a lot of air resistance*. A person without a parachute falls faster because less air pushes against them. |
The faster something falls, the more air resistance there is on it. Eventually, the air resistance slowing it down becomes as strong as the pull of gravity. Then its speed no longer changes. This is called terminal speed. |
|
Free fall If there were no air, there would be no air resistance. All falling objects would just get faster and faster < called is This rate. same the> free fall. | |
67. Falling objects are pulled down to the ground by .
A. gravity B. resistance C. speed D. acceleration（加速度）
68. Why do people make parachutes（降落伞）?
A. To look pretty and colourful in the air. B. To slow down the falling speed.
C. To push against the air in the sky. D. To accelerate the falling movement.
69. Which did Galileo discover?
A. A heavy ball falls faster than a light ball. B. A light ball falls faster than a heavy ball.
C. A light ball and a heavy ball fall at the same speed
D. A light ball and a heavy ball fall at different speed.
70. Which of the following is NOT true according to the passage？
A. Heavy and light objects fall equally when they are different in size.
B. When air resistance equals gravity, objects fall at terminal speed.
C. Without air; all falling objects get faster and faster at the same rate.
D. Slippers（拖鞋） and boots （靴子）fall at the same speed because they have the same shape
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D
The price of gas has been going up. We do not know when it will end. Many people want to know how they can save gas. The best way to save gas is to change driving habits.
The accelerator (加速器) or gas pedal, has a lot to do with how much gas you use. The faster you drive, the more gas you use. Drivers should slow down a bit to save gas. Driving at a steady speed helps to save much gas you use. Accelerating slowly to get to the speed you want to go helps save gas too.
The more you drive your car, the more gas you use. Think about the places you need to go before leaving your home. You should run as many errands (差事) that you need to do in one trip. Always try to pick the shortest route when going somewhere.
Cars that are in good working condition use less gas. Take care of your car. Make sure the engine is running well and is tuned up often. Have a repairman check it if something seems wrong.
Tires are important too. Keep the tires inflated (饱满) properly on a car. It will help the car roll better and will get you better mileage （英里数） If the tires of a car are worn then they should be replaced.
Finally, think about using your car less. Walk or ride a bike if you do not have far to go. Carpool (合伙用车) or take public transportation when you can. Leaving your car at home really saves gas.
There are many ways a person can save gas. These are just a few ideas that can help you save some money at the gas pump. Try changing the way you drive and see how much it saves you!
68. Which of the following can help save gas?
A. Driving as fast as you can.
B. Accelerating quickly to get to the speed you want.
C. Driving fast a little now and slowly a little then.
D. Driving at a speed that is, seldom changed.
69. The underlined sentence in the 3rd paragraph probably means you should
A. do as many things as you can in one trip
B. go to as many places as you can in one trip
C. take as many people as you can in one trip
D. use as many ways of driving as you can in one trip.
70. Which of the following is NOT true according to the passage?
A. Always keep your car in good working condition. B. Never use your car unless it is necessary.
C. Replace your tires if they are worn out. D. Always stick to your own driving habits.
71. Which would be the best title for the passage?
A. How to use your car correctly.
B. How to save gas when using your car.
C. How to deal with the price of gas.
D. How to form good driving habits.
D
The price of gas has been going up. We do not know when it will end. Many people want to know how they can save gas. The best way to save gas is to change driving habits.
The accelerator (加速器) or gas pedal, has a lot to do with how much gas you use. The faster you drive, the more gas you use. Drivers should slow down a bit to save gas. Driving at a steady speed helps to save much gas you use. Accelerating slowly to get to the speed you want to go helps save gas too.
The more you drive your car, the more gas you use. Think about the places you need to go before leaving your home. You should run as many errands (差事) that you need to do in one trip. Always try to pick the shortest route when going somewhere.
Cars that are in good working condition use less gas. Take care of your car. Make sure the engine is running well and is tuned up often. Have a repairman check it if something seems wrong.
Tires are important too. Keep the tires inflated (饱满) properly on a car. It will help the car roll better and will get you better mileage （英里数） If the tires of a car are worn then they should be replaced.
Finally, think about using your car less. Walk or ride a bike if you do not have far to go. Carpool (合伙用车) or take public transportation when you can. Leaving your car at home really saves gas.
There are many ways a person can save gas. These are just a few ideas that can help you save some money at the gas pump. Try changing the way you drive and see how much it saves you!
68. Which of the following can help save gas?
A. Driving as fast as you can.
B. Accelerating quickly to get to the speed you want.
C. Driving fast a little now and slowly a little then.
D. Driving at a speed that is, seldom changed.
69. The underlined sentence in the 3rd paragraph probably means you should
A. do as many things as you can in one trip
B. go to as many places as you can in one trip
C. take as many people as you can in one trip
D. use as many ways of driving as you can in one trip.
70. Which of the following is NOT true according to the passage?
A. Always keep your car in good working condition. B. Never use your car unless it is necessary.
C. Replace your tires if they are worn out. D. Always stick to your own driving habits.
71. Which would be the best title for the passage?
A. How to use your car correctly.
B. How to save gas when using your car.
C. How to deal with the price of gas.
D. How to form good driving habits.
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D
The price of gas has been going up. We do not know when it will end. Many people want to know how they can save gas. The best way to save gas is to change driving habits.
The accelerator (加速器) or gas pedal, has a lot to do with how much gas you use. The faster you drive, the more gas you use. Drivers should slow down a bit to save gas. Driving at a steady speed helps to save much gas you use. Accelerating slowly to get to the speed you want to go helps save gas too.
The more you drive your car, the more gas you use. Think about the places you need to go before leaving your home. You should run as many errands (差事) that you need to do in one trip. Always try to pick the shortest route when going somewhere.
Cars that are in good working condition use less gas. Take care of your car. Make sure the engine is running well and is tuned up often. Have a repairman check it if something seems wrong.
Tires are important too. Keep the tires inflated (饱满) properly on a car. It will help the car roll better and will get you better mileage （英里数） If the tires of a car are worn then they should be replaced.
Finally, think about using your car less. Walk or ride a bike if you do not have far to go. Carpool (合伙用车) or take public transportation when you can. Leaving your car at home really saves gas.
There are many ways a person can save gas. These are just a few ideas that can help you save some money at the gas pump. Try changing the way you drive and see how much it saves you!
68. Which of the following can help save gas?
A. Driving as fast as you can.
B. Accelerating quickly to get to the speed you want.
C. Driving fast a little now and slowly a little then.
D. Driving at a speed that is, seldom changed.
69. The underlined sentence in the 3rd paragraph probably means you should
A. do as many things as you can in one trip
B. go to as many places as you can in one trip
C. take as many people as you can in one trip
D. use as many ways of driving as you can in one trip.
70. Which of the following is NOT true according to the passage?
A. Always keep your car in good working condition. B. Never use your car unless it is necessary.
C. Replace your tires if they are worn out. D. Always stick to your own driving habits.
71. Which would be the best title for the passage?
A. How to use your car correctly.
B. How to save gas when using your car.
C. How to deal with the price of gas.
D. How to form good driving habits.
查看习题详情和答案>>