Balanced & Unbalanced Forces | Forces & Motion | Physics | FuseSchool

Balanced & Unbalanced Forces | Forces & Motion | Physics | FuseSchool

How do we find out whether the forces acting on an object are balanced or unbalanced? Learn in this video from the "Forces and Motion" chapter of the FuseSchool GCSE / K12 Physics.

00:00 - Introduction
Balanced forces. The famous English scientist Sir Isaac Newton, who lived between the 17th and 18th century, devised three laws of motion.

00:13 - Balanced forces
The first law states that if all the forces acting on an object are balanced, there will be no acceleration; meaning either constant velocity or the object remaining stationary but, what do we mean by balanced forces?

00:27 - Example
Let's look at the example of a horse. The first force we will consider is the force of gravity, this acts towards the centre of the earth. The size of the force of gravity is the horses weight. An arrow is drawn downwards from the horse towards the centre of the earth. If this were the only force acting on the horse, it would sink into the ground. As this is not the case, there must be a force opposing the force of gravity and arrows drawn in the opposite direction but equal in size.

01:00 - Reaction force
This force is called the reaction force. As the reaction force is the same size, but acts in the opposite direction to the horse's weight, these two forces are a balanced pair of forces. There are other forces acting on the horse.

01:17 - Other forces
The horse is moving forward, and therefore there must be a driving force from the horse's legs. The driving force though is opposed by forces trying to slow the horse down, and if the horse is traveling at a constant velocity, the force of friction and air resistance are equal in size, but opposite in direction to the driving force. The driving force is now balanced by friction and air resistance, a balanced pair of forces, and the horse now travels a constant velocity.

01:50 - Unbalanced forces
If though the horse accelerates the driving, force must be greater than friction and air resistance - the driving force is now no longer balanced by friction and air resistance. These forces are now unbalanced.

02:06 - Summary
So in summary, when the forces are balanced on an object - the object will either remain stationary or travel at velocity. When the forces are unbalanced, the object will either accelerate, meaning an increase in velocity, or decelerate, meaning a decreasing velocity.


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