jee main forms 2014
SCIENCE IN EVERYDAY LIFE PART- 2
The holding belts of a schoolbag are wide
Pressure is thrust per unit area. For a given thrust (force perpendicular to the surface), the greater the area on which the force acts, the less is the pressure due to the force. The holding belts of a school bag are made wide so that the pressure due to the weight of the schoolbag is reduced by increasing the area. It is then easier to bear the load of the bag.
A sheet of metal that sinks in water can float if shaped like a pan.
A sheet of metal sinks in water because its density is more than that of water. If the sheet is shaped like a pan, it can displace a large amount of water such that the upthrust on the pan due to water balances the weight of the pan. Hence, it can float on water.
A ship entering fresh water from sea water sinks more.
The buoyant force due to liquid is proportional to the density of the liquid. Hence, the volume of the liquid displaced by a floating body is inversely proportional to the density of the liquid. The density of freshwater is less than that of seawater. Hence, a ship displaces a greater volume of fresh water relative to that of seawater. Therefore, a ship entering fresh water from sea water sinks more.
A pointed nail can be easily hammered into wood than a blunt nail.
Pressure varies inversely as the area of the surface on which the force is applied, if the force remains constant. The tip of a pointed nail has extremely small area while that of a blunt nail has a comparatively large area. Therefore, a given force creates a large pressure on the pointed nail and it can be easily hammered into the wood, while a very less pressures is produced on the blunt nail by the same force and it cannot be easily hammered into the wood.
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INTERESTING Q & A
Why do we fall sideways when we are sitting in a bus and it takes a sharp turn?
When we sit in a bus and the bus is in motion, we are in a state of motion in the same direction. When the bus takes a sharp turn, our body tends to maintain the state of motion in the straight line due to inertia. The portion of our body in firm contact with the seat acquires the motion along the curved path, but the upper portion of our body, in loose contact with the seat, tends to move in the initial direction of motion. Hence, we fall sideways.
What happens when you shake a wet piece of cloth? Explain your observation.
When we shake a wet piece of cloth, water droplets come out. Initially, the wet piece of cloth is at rest. When the cloth is shaken, it is accelerated, but the water droplets in it, due to inertia, tend to maintain the state of rest. Hence, the droplets come out.
If brakes are suddenly applied to a moving car, the passengers in the car are pushed in the forward direction. Explain why.
The passengers in a moving car have the same velocity as that of the car. When brakes are suddenly applied to the car, it stops suddenly and the lower parts of the passengers’ bodies in contact with the seats, come to rest. The upper parts of their bodies, however, continue to be in a state of motion due to inertia. Hence, the passengers are pushed in the forward direction.
We get a backward push when the bus starts at one. Explain why.
When we sit or stand in a stationary bus, we are in a state of rest. When the bus starts suddenly, the lower parts of our bodies in contact with the bus acquire the motion of the bus. The upper parts of our bodies, however, continue to be in the state of rest due to inertia. Hence, we get a backward push when the bus starts at once.
A person alighting from a moving train is likely to fall in the direction of motion of the train. Explain why.
A person in a moving train has the same velocity as that of the train. After alighting from the moving train his feet come to rest on the platform. However, due to inertia, the upper part of his body continues to be in a state of motion in the direction of motion of the train. Hence, he is likely to fall in the direction of motion of the train.
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POINTS TO PONDER
Distance and displacement are different concepts.
Distance is the length of the actual path followed by a body between the points under consideration. It can be greater than the length of the straight line joining the two points. i.e. the initial and the final points. It does not involve the concept of direction.
Displacement is the shortest distance from the initial point to the final point of movement of a body. It involves the concept of direction. It, therefore, follows that distance and displacement are different concepts.
An object at rest can be considered to have uniform motion.
An object is said to be in uniform motion when it has constant speed. For an object at rest, its speed is zero all the time. Hence, an object at rest can be considered to have uniform motion.
When a body falls freely to the ground, its motion has a uniform acceleration
When a body falls freely, the only force acting on the body is that due to gravity. Near the earth’s surface, this force on a given body is (practically) uniform. Hence, a body falling freely to the ground has (almost) a uniform acceleration.
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