Back to: Jss1 Basic Science (BST)

Topic: Calculation Of Gravitational Force

WEEK: 3 & 4

People learned about gravity after Isaac Newton found out what it was. Also, these days, everyone knows what gravity is. But do you also know that everything in the universe is pulling on you right now? So, if you want to learn more, read about gravitational force, the gravitational force formula, how the formula was made, and a solved example.

To calculate the force of gravity acting on a ball thrown up;

F = mg

Where F = the force acting on the ball in Newton (N).

m = mass of the ball in kilograms (kg).

g = acceleration due to gravity in metres per second square (m/s^{2}).

This has a standard value of 9.8 m/s^{2}.

F = mg

N = kg x m/s^{2 }N = kgm/s^{2} or kgms^{2}

Example 1

What is the gravitational force acting on an object of mass 50 kg?

Solution

F = mg

F =?

m = 50 kg

g = 9.8 m/s^{2}

F = 50 kg x 9.8 m/s^{2}

^{ }F = 490 kgm/s^{2}

Therefore, F = 1,960 N

(Note: N = kgm/s^{2})

Example 2

Calculate the gravitational force required to pull down an object of 100kg falling with an acceleration of 10m/s^{2}.

Solution:

F = mg,

F = ?

m = 100kg,

a = 10m/s^{2}

∴ F = 100 × 10 = 1000 N.

F= 1000 N.

(Note: N = kgm/s^{2})

## Setting up a balanced force

When two equal and opposite forces act on a body, this is called a balanced force. A balanced force is acting on something that is not moving. When forces that are equal and opposite act on an object, the object is said to be static, or in equilibrium. A cup sitting on a table is affected by two forces that pull in opposite directions but are equal in strength. The earth’s gravity pulls the cup down, while the cup’s own weight pulls it up.

Another example is the game of tug-of-war. When the people on each side of the rope pull with the same force, but in the opposite direction, the forces are balanced. Because of this, nothing moves.