(a) What is the difference between the density and relative density of a
(b) If the relative density of a substance is 7.1, what will be its density in SI
(a) The density of a substance is defined as
SI unit of density is kg/m3
The relative density of a substance is the
It has no unit.
Define thrust. What is its
The force acting on a body perpendicular to its surface is called thrust. The SI unit of thrust is newton (N).
A mug full of water appears light as long as it is
A mug full of water appears light as long as it is under water because buoyant force acts on it which reduces its effective weight and makes it appear lighter.
What happens to the buoyant force as more and more volume of a solid object is immersed in a
As more and more volume of the solid object is immersed in the liquid, the upward ‘buoyant force’ also keeps on increasing. When the object is completely immersed in the liquid, the buoyant force acting on the solid becomes maximum and remains constant thereafter.
Why do we feel light on our feet when standing in a swimming pool with water up to our
As more and more volume of our body is immersed in water, the apparent weight of the body goes on decreasing and the body seems to become lighter. This is due to the increase in upward buoyant force acting on the body.
An iron nail sinks in water but it floats in mercury.
An iron nail sinks in water but it floats in mercury because
Explain why, a piece of glass sinks in water but it floats in mercury.
A piece of glass sinks in water but it floats in mercury because
Steel sinks in water but a steel boat floats.
A piece of steel sinks in water because steel is denser than water. However, a steel ship is a hollow object made of steel and contains a lot of air in it. Due to
School bags have wide straps so that their weight may spread over a large area of shoulder producing less pressure on the shoulder.
Why does a sharp knife cut objects more effectively than a blunt
A sharp knife cuts objects easily because due to its very thin edge, the force of our hand falls on a very small area of the object producing large pressure.
Explain why, wooden (or concrete) sleepers are kept below the railway line.
Concrete or wooden
sleepers are kept below the railway line so that the weight of passing
is spread over a large area of ground and the track may not sink into the
The density of iron or steel is much higher than that of water, so an object made of iron or steel (like this car) sinks in water.
A wide steel belt is provided over the wheels of an army tank so that they exert less pressure on the ground and do not sink into it.
The tip of the sewing needle is sharp so that due to its sharp tip, the needle may put the force on a very small area of the cloth, producing a large pressure sufficient to pierce the cloth being stitched.
When is the pressure on the ground more—when a man is walking or when a man is
When a man is walking, then at one time only one foot is on the ground. Due to this, the force of
Explain why, when a person stands on a cushion, the depression is much more than when he lies down on it.
When a person stands on a cushion then only his two feet (having small area) are in contact with the cushion. Due to
Use your ideas about
Flat shoes have
A nail has a pointed
|1. What is the formula for gravitational force?
|2. What is the value of the gravitational constant?
|3. How does the gravitational force vary with distance?
|4. What is the difference between mass and weight?
|5. What is the significance of the law of universal gravitation?