8th Class Science Force and Pressure Tension Force

       Tension Force

When an object is hanged with the help of a rope, a force is transmitted through the rope, called tension force. It always acts along the length of the rope, and is pulled equally on the objects in the opposite direction. Let us consider the surface of water. If you observe the upper surface of water carefully, you will find that, it behaves like an elastic surface. This is because of the fact, that there is intermolecular force of attraction between the molecules of water, which holds the molecules together. This force is called surface tension.

       Thomas gently places a coin on the surface of water in the bucket, and finds that it does not sink in the water. It shows that the surface is behaving like a elastic surface. The reason for this behavior of the surface is _________.

(a) Nuclear force

(b) Electrostatic force

(c) Intermolecularforce

(d) Gravitational force

(e) None of these

Answer: (c)

Explanation

The surface of water behaves like an elastic surface, because there is intermolecular force between the molecules of water.

     David mixes a drop of water in the cup containing mustard oil. He observes that it changes into the shape of a spherical ball. What could be the possible reason for this?

(a) Surface tension

(b) Viscosity  

(c) Density

(d) Surface area

(e) None of these

Answer: (a)

Explanation

When the oil is mixed in water, it becomes spherical. It is because of the surface tension between the molecules of the oil drop.

           Muscular Force

To lift a table from the ground to a certain height, we need to apply a force; or if you want to throw a cricket ball, also you have to apply a force. These forces are exerted by the muscles of our arm or body. The force applied by the muscles of our body is known as the muscular force. The muscular force depends upon the strength of the body or the mass of the object. Human use the muscular force of the animals to do various work. For example, ploughing of the field by an ox, or carrying of loads from one place to another by camels or donkey.

        A weight lifter lifts the weight with the help of his hand, and has to apply large force to do this. The force, which the weight lifter has to apply to lift the weight is called _______.

(a) Cellular force

(b) Nuclear force

(c) Muscular force

(d) Magnetic force

(e) None of these

Answer: (c)

Explanation

The force applied by our body to do any type of work, is a muscular force.

       A boy is pulling the cart on the road, in the process he is using his muscular energy. The muscles get its energy form the body in the form of glucose. From where does, the body derives it energy_______.

(a) Sunlight

(b) Tissues

(c) Cell      

(d) Food

(e) None of these

Answer: (d)

Explanation

The body derives its energy from the food we eats..