Science: Forces in action

                                                Force in Action

Q 1 Explain the construction and working of Manometer.

Ans.  Manometer is a device which is used to measure the pressure exterted by liquids.

Construction :  It consists of a U-tube made of glasses or transparent polythene with both its ends open, fixed vertically on a stand. Filled with colored water or mercury. A plastic funnel is fixed at one end of the tube and covered with rubber balloon sheath.

Working :  When dipped inside the container having liquid in it the level of mercury changes and the difference between the initial and final level of the mercury shows the pressure exerted by the liquid.

Q2 Give two examples each of situation in which you push or pull to change the state of motion of objects.

Ans . Two examples of push force are as follows :

- A heavy box at rest is pushed to move it from one room to another. This changes the state of motion of the box.

- A player pushes a football using his foot. This changes the state of the motion of the ball.

           Two examples of pull forces are as follows :

        - Rope is pullled to draw water from a well. This changes the state of motion of the water bucket.

        - A drawer is pulled to open it. This changes the state of motion of the drawer.

Q3 . A blacksmith hammers a hot piece of iron while making a tool. How does the force due to hammering affect the piece of iron?

Ans. The force of hammering changes the shape of iron in the form of desired tool.

Q4 . Name the forces acting on a plastic bucket containing water held above ground level in your hand. Discuss why the forces acting on the bucket do not bring a change in its state of motion.

Ans. The forces that act on the bucket are as follows :-

1) The pressure of water contained in it.

2)  Force of gravity due to Earth’s gravitation

Pressure of water can not change the state of motion because it is inside the bucket and force of gravity is compensated by force applied vertically upward using rope.

Q5 A rocket has been fired upwards to launch a satellite in its orbits. Name the two forces acting on the rocket immediately after leaving the launching pad.

Ans.  The two forces acting on rocket are :

- Force due to gravity acts vertically downward.

- Frictional force of atmosphere.

Q6. It is difficult to cut cloth using a pair of scissors with blunt blades. Explain.

Ans.  Blunt blades have a larger area as compared to the area of sharp-edged blades. Thus, the force applied on blunt blades produces a lower pressure. The low pressure of the blunt blades makes it difficult to cut the cloth.

Explaination :  The area over which the muscular force is applied has an important role in determining the relative difficulty or ease of the task which makes use of the muscular force. The smaller the area of contact, the larger will be the pressure on the surface for the same force, and hence, the less difficult will be the task.

Q 7. It is much easier to burst an inflated balloon with a needle than by a finger. Explain.

Ans . When we prick the surface of an inflated balloon with a needle, the needle exerts a larger pressure because it has a smaller area of contact compared to that of the finger. The large pressure exerted by a needle pierces the surface of the inflated balloon easily.

Q8. Two thermocol balls held close to each other move away from each other. When they are released, name the force which might be responsible for this phenomenon. Explain.

Ans.  Electrostatic force is responsible for this phenomenon. When thermocol balls having similar charges are released, they move away from each other due to the repulsive telectrostatic forces between the similar kinds of charges.

Explaination :  Like charges repel each other whereas unlike charges attract each other.

Q9 . A man is pushing a cart down a slope. Suddenly the cart starts moving faster and he wants to slow it down. What should he do?

Ans.  When the man is pushing the cart down the slope, the force of gravity also acts on the cart. The net force acting on the cart increases and hence, the cart starts moving faster down the slope.

The man should apply an opposing force to decease the net force acting on the cart. Instead of pushing the cart, he should try to pull the cart up the slopes so that the cart slows down.