Earth’s Gravitational Acceleration

The gravitational force due to the earth on a body results in its acceleration. This is called acceleration due to gravity and is denoted by ‘g’. Acceleration is a vector.

Gravitational force is the force that the Earth uses to pull all objects toward itself. This is why when something is thrown upward, it eventually falls back down to the ground.

• For example, when a ball is thrown up, it reaches a certain height and then comes back down because of the Earth's gravitational pull.
• The stronger the gravitational force on an object, the harder it is to lift.
• Gravitational force also works in space. It keeps the planets in the solar system revolving around the sun.
• Gravity also acts between planets and their moons, keeping the moons in orbit around the planets.

Discovery of Gravitational Force:

In the 17th century, Sir Isaac Newton discovered the concept of gravitation. The earth’s gravitational force acts in a direction opposite to that of an object moving upwards. Hence, the speed of that object goes on decreasing till, in the end, it becomes zero. Then the object starts falling down instead of going up any further. While falling, its speed goes on increasing all the time due to gravitational force.

The Earth attracts all objects towards its centre due to gravitational force. The centre of mass of the Earth is at its geometric centre, so the gravitational force on any object is always directed toward the centre of the Earth.

• This force causes objects to fall vertically downward when dropped.
• When a stone is thrown upwards, gravity pulls it down, gradually reducing its velocity. Eventually, the velocity becomes zero, and the stone starts falling back due to Earth's pull.

Gravitational Force and the Moon/Satellites:

• The Earth’s gravity also acts on the Moon and artificial satellites, keeping them in orbit.
• Unlike a falling object, the Moon and satellites do not crash into Earth because they have a forward velocity along their orbits.
• If this velocity did not exist, they would fall directly onto Earth, just like an apple falling from a tree.

Thus, the balance between Earth’s gravitational pull and the orbital velocity keeps the Moon and satellites in continuous motion around Earth.

1. Aim: To observe the difference in sound when a stone is dropped from different heights and understand the effect of gravitational force on objects of different weights. Effect of Height and Weight on Gravitational Force.

2. Requirements: A small stone, a bucket of water, and two sacks (one empty, one full)

3. Procedure

I. Stone experiment:

• Take a small stone and a bucket of water.
• Drop the stone into the water from a height of about 20 cm.
• Observe and listen to the sound made when the stone hits the water.
• Now, drop the same stone into the water from a height of about 100 cm.
• Again, observe and listen to the sound produced.

II. Sack experiment:

• Take two sacks—one empty and the other full.
• Lift the empty sack and notice how much effort is needed.
• Then, lift the full sack and observe the difference in the effort required.

4. Conclusion:

1. For the stone experiment: Dropping the stone from a greater height produces a louder sound because the stone gains more speed as it falls due to the effect of gravitational force. This means that the greater the height, the more speed and force the stone has when it hits the water.
2. For the sack experiment: The empty sack is easier to lift because it weighs less, meaning the gravitational force acting on it is smaller. The full sack requires more effort to lift because it is heavier, and the gravitational force on it is greater. This shows that greater force is needed to lift heavier objects.

 Dropping a stone in water

Carrying a load