1. Why does a rider feel a tendency to fall when the horse starts running of stops suddenly?
Ans: This is caused by inertia. When the horse starts running, the rider, being at rest, falls back. When a running horse stops suddenly, the rider being in motion has a tendency to fall ahead.
2. Why does a person carrying a bucket full of water in his right hand bend towards the left?
Ans: He bends towards his left so that the centre of gravity falls within the base. This enables him to keep up balance, otherwise he may fall.
3. Why does tea cool more rapidly in a saucer than in a cup?
Ans: In a saucer evaporation takes place more rapidly than in a cup. Cooling is caused by evaporation.
4. Ice packed in sawdust does not melt quickly. Why?
Ans: Ice packed in sawdust does not melt quickly, because sawdust being bad conductor, it cuts the heat rays.
5. Why do you heat a metal rim before fitting it to a wheel?
Ans: By heating, the rim expands and fits easily over a slightly bigger radius than that of the rim. On being cooled it contracts and has a firm grip on the wheel.
6. Why do wet clothes dry slowly on a rainy day?
Ans: On a rainy day the atmosphere air contains more water vapor than on a dry day and hence evaporation is slower.
7. Why does a substance thrown up come to the ground?
Ans: Because of the gravitational force of the earth.
8. Why does moisture gather outside of a glass of cold water on a warm day?
Ans: The temperature of the outer surface of glass of cold water is lower than that of its surroundings. The vapor in the surrounding atmosphere gets condensed on the outer surface of the water appears in the forms of tiny particles of water.
9. What happens to iron when it rusts?
Ans: It reacts with the oxygen of the air and forms iron-oxide which is the rust.
10. How would you distinguish between welding and soldering?
Ans: Welding is the joining of metals by raising the temperature of the metals to fuse them together by melting their ends. Soldering is the joining of metals with the help of an alloy called solder.
11. How does a ball which falls down, bounce up?
It is due to the operation of Newton’s Third Law of motion. To every action there is equal and opposite reaction. A ball falling to the ground is slightly deformed. Due to the elastic force of the material of which the ball is made, the ball tries to recover its original shape. In doing so it forces the ground which pushes the ball upward due to reaction and the ball bounces up.
12. An iron nail floats on mercury but sinks in water. Give reasons.
Ans: The specific density of iron is lower than of mercury, hence it floats on mercury, while it is higher than that of water, and hence it sinks in water.
13. How do you convert Centigrade in to Fahrenheit?
Ans: With the help of the following formula – C/100 = F-32/180
14. It is advisable to work electric appliances when they are earthed suitably. Why?
Ans: In case of short-circuiting, the current passes to the earth without harming the user, if an electrical appliance is properly earthed.
15. How does a refrigerator keep food fresh?
Ans: Food is kept fresh so long as fermentation does not set in; refrigeration prevents fermentation by providing low temperature.
16. Ice wrapped in a blanket does not melt away quickly. Why?
Ans: Blanket being bad conductor of heat prevents the outside heat from creeping inside.
17. Why can a petrol fire not be extinguished by throwing water on it?
Ans: The heat of the petrol fire is so intense that the water thrown on it gets evaporated and decomposed. Hence it is not effective in extinguishing the petrol fire.
18. A train stops when the chain is pulled. Why?
Ans: When the chain is pulled, one small valve gets opened and air/atmospheric pressure is admitted to the under side of the piston head of the brake cylinder through pipe connection. Initially there is vacuum on both top and bottom side of the piston head. When the air/atmospheric pressure enters the under side of the piston head, the piston raises up due to difference of pressure and pulls the brake rigging to which it is connected with links and levers. Thus the brakes are applied and the train stops.
Ans: This is caused by inertia. When the horse starts running, the rider, being at rest, falls back. When a running horse stops suddenly, the rider being in motion has a tendency to fall ahead.
2. Why does a person carrying a bucket full of water in his right hand bend towards the left?
Ans: He bends towards his left so that the centre of gravity falls within the base. This enables him to keep up balance, otherwise he may fall.
3. Why does tea cool more rapidly in a saucer than in a cup?
Ans: In a saucer evaporation takes place more rapidly than in a cup. Cooling is caused by evaporation.
4. Ice packed in sawdust does not melt quickly. Why?
Ans: Ice packed in sawdust does not melt quickly, because sawdust being bad conductor, it cuts the heat rays.
5. Why do you heat a metal rim before fitting it to a wheel?
Ans: By heating, the rim expands and fits easily over a slightly bigger radius than that of the rim. On being cooled it contracts and has a firm grip on the wheel.
6. Why do wet clothes dry slowly on a rainy day?
Ans: On a rainy day the atmosphere air contains more water vapor than on a dry day and hence evaporation is slower.
7. Why does a substance thrown up come to the ground?
Ans: Because of the gravitational force of the earth.
8. Why does moisture gather outside of a glass of cold water on a warm day?
Ans: The temperature of the outer surface of glass of cold water is lower than that of its surroundings. The vapor in the surrounding atmosphere gets condensed on the outer surface of the water appears in the forms of tiny particles of water.
9. What happens to iron when it rusts?
Ans: It reacts with the oxygen of the air and forms iron-oxide which is the rust.
10. How would you distinguish between welding and soldering?
Ans: Welding is the joining of metals by raising the temperature of the metals to fuse them together by melting their ends. Soldering is the joining of metals with the help of an alloy called solder.
11. How does a ball which falls down, bounce up?
It is due to the operation of Newton’s Third Law of motion. To every action there is equal and opposite reaction. A ball falling to the ground is slightly deformed. Due to the elastic force of the material of which the ball is made, the ball tries to recover its original shape. In doing so it forces the ground which pushes the ball upward due to reaction and the ball bounces up.
12. An iron nail floats on mercury but sinks in water. Give reasons.
Ans: The specific density of iron is lower than of mercury, hence it floats on mercury, while it is higher than that of water, and hence it sinks in water.
13. How do you convert Centigrade in to Fahrenheit?
Ans: With the help of the following formula – C/100 = F-32/180
14. It is advisable to work electric appliances when they are earthed suitably. Why?
Ans: In case of short-circuiting, the current passes to the earth without harming the user, if an electrical appliance is properly earthed.
15. How does a refrigerator keep food fresh?
Ans: Food is kept fresh so long as fermentation does not set in; refrigeration prevents fermentation by providing low temperature.
16. Ice wrapped in a blanket does not melt away quickly. Why?
Ans: Blanket being bad conductor of heat prevents the outside heat from creeping inside.
17. Why can a petrol fire not be extinguished by throwing water on it?
Ans: The heat of the petrol fire is so intense that the water thrown on it gets evaporated and decomposed. Hence it is not effective in extinguishing the petrol fire.
18. A train stops when the chain is pulled. Why?
Ans: When the chain is pulled, one small valve gets opened and air/atmospheric pressure is admitted to the under side of the piston head of the brake cylinder through pipe connection. Initially there is vacuum on both top and bottom side of the piston head. When the air/atmospheric pressure enters the under side of the piston head, the piston raises up due to difference of pressure and pulls the brake rigging to which it is connected with links and levers. Thus the brakes are applied and the train stops.
Courtesy: Articlediary.com
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