Gravitational Force

Experiment to locate the centre of gravity to determine the stability of the body and relate its significance in everyday experiences.

- location of C.G, relation of position of C.G and area of base of support with stability.

-definition and application of stable, unstable, and neutral equilibrium.

1. Investigate the location of the center of gravity to relate with stability of bodies.

2. Demonstrate three types of equilibrium to relate it to the real life application.

What is Gravity?

The force by which a planet or other body draws objects toward its center.

ALL matter that has MASS or ENERGY has Gravitational Pull.

What makes Gravitational Pull Stronger?

Mass and Distance

Centre of Gravity (CG)

Centre of gravity of a body is defined as a point of application of the resultant force due to the earth's attraction on it.

The centre of gravity of a body is the point where the whole weight of the body can be considered to act.

For all regular shape bodies, the geometric center is the Centre of gravity.

For irregular shape lamina, the intersection of lines of action is the Centre of gravity.

Stability of Bodies:

The stability of a body is determined by-

1. Position of C.G. of a body

2. Area of the Base of Support (B.S.)

• The body is more stable if the position of C.G. is at its lower part.

• If line of gravity due to the weight of body acts vertically downward through its base, then the body is considered as stable. Therefore larger the base of support, more stable the body is.

Stable Equilibrium

• ability to regain its original position even when displaced by an external force.

• C.G. comes it back to its initial position.

Unstable Equilibrium

• loses its ability to regain its original position when displaced by an external force.

• A body with narrow B.S. and C.G at high position is usually unstable

• takes up new position which has lower C.G.

Neutral Equilibrium

• neither takes a new position nor regains its original position when displaced by an external force

• the position of the C.G. and B.S. do not change

Here are some examples showing how the stability of a body depends on the position of its center of gravity (CG).

1. Racing cars are built low and with wide wheelbases to reduce the risk of overturning at sharp bends.

2. While crossing a river in a boat, passengers are not allowed to stand. This keeps the CG of the system (boat and passengers) low and ensures stability.

3. In a double-deck bus, more passengers are allowed on the lower deck than on the upper deck. Moreover, standing is not allowed in the upper deck. This is done to keep the CG fairly low to ensure the stability of the double-deck bus.

4. A person has to bend forward while going uphill and backward while coming down. He bends in order to keep the vertical line passing through his CG always between his feet, thereby increasing his stability.

5. In an advanced stage of pregnancy, women develop back pains. The CG of a pregnant woman extends forward, beyond the area bounded by her feet. To maintain her balance she extends her upper body backward to bring her CG above her feet, which in turn often causes back pain.

6. Tall lamp stands have heavy bases so that the CG is low.

7. A porter carrying a load on his back leans forward to keep the vertical line passing through the CG of the system (load plus himself) between his feet.

1. Why would you advice a person to sit rather than stand in a moving bus?

2. “The centre of gravity of a body may not be necessarily on the body”. Justify.

3. Why do dzongs have broader base?

4. Explain the following terms:

• (i) Stable Equilibrium

• (ii) Unstable Equilibrium

• (iii) Neutral Equilibrium

5. What are the factors that determines the stability of a body ? Explain how each effects the stability.

6. What is gravitational field?

7. What are the factors determines the force of gravity acting between the bodies? Explain how each effects the force.

8. Write difference between stable equilibrium and unstable equilibrium.

9. Why are the number of passengers allowed to stand on the top deck of a double decker bus limited?

10. If you are planning to construct chorten for the well being of all living being that would last for centuries, how would you make it more stable so it can withstand any earthquake.