The concept of force is an important topic related to basic physics. A force is simply the push or pull that occurs when an object interacts with other things in its surroundings. Forces can cause objects to stay still, to move at a set rate, to speed up, or to slow down. The impact a force has on an object is based on whether the force is balanced or unbalanced. Discover basic facts about balanced and unbalanced forces.
Forces that are balanced are ones that are equal in size and opposite in direction. Since one force is not stronger than the other, the motion of the object that the forces are acting upon does not change. This results in what is called unchanging motion.
- If the object was not moving to start with, being acted upon by balanced forces will not cause it to move. The object will remain at rest.
- If the object was moving prior to interacting with balanced forces, the motion will not change. The speed and direction of the object's motion will stay the same.
In essence, the push or pull of one force ends up being canceled out by the other force because both forces are equivalent.
When forces are unbalanced, that means the opposing forces are not the same in magnitude — one is stronger than the other. An object is subject to unbalanced forces when a force applied in one direction exceeds the force that is applied in another direction.
- When unbalanced forces are applied to an object that is sitting still, the object will move in the direction pushed or pulled by the stronger force.
- When unbalanced forces are applied to an object that is moving, the direction and/or speed with which the object is moving will change.
With unbalanced forces, the stronger force wins out over the weaker one and causes a change in motion for the object.
Many examples of balanced and unbalanced forces can be seen in everyday life.
Anything that is not moving or that continues moving at a fixed speed in the same direction is experiencing balanced forces.
- an object floating in water
- a tug of war game where neither side is winning
- doing a handstand or headstand (without falling)
- a running car staying in place because the brakes are applied
- planets orbiting the sun in a fixed orbit
- a person standing or sitting still
- a vehicle that continues moving at the same speed
- framed pictures hanging on a wall
- a jacket hanging on a coat hook
Any object that changes the speed or direction of its motion or moves after being at rest is experiencing unbalanced forces.
- an object sinking in water
- a group of kids winning a tug of war game
- turning a cartwheel
- a car accelerating, braking or turning
- riding a skateboard
- a fruit dropping from a tree
- an object getting knocked over by the wind
- a football sailing toward the goalpost after it is kicked
- a moving train that slows down prior to stopping
Test your knowledge by answering the practice questions below. Don't peek at the answers until you have tried to answer each question on your own.
For each item, determine if the forces described are balanced or unbalanced.
- tossing a rock so that it skips against the water
- an item rolls off a surface it was placed on
- a computer monitor stays in place on a desk
- a swing swaying in the breeze
- a figure skater does a double axel
- a backpack hanging from a hook
- a bicycle being ridden at a set speed down a straight road
- unbalanced - The rock slows down every time it skips until it sinks.
- unbalanced - Gravity overcomes friction between the item and the table.
- balanced - The monitor has no change in its motion — it just sits there.
- unbalanced - The swing moves back and forth as gravity pulls it down, and the breeze pushes it forward and up.
- unbalanced - The skater moves in a circle (rotation) until the friction between the ice and the skates finally stops the rotation.
- balanced - The force attaching the hook to the wall (either screws, nails or glue) is balanced with the force of gravity.
- balanced - The bike is not changing speed or direction, so the force of friction between the tires and the road is balanced by the force you put into the pedals. (Also, the rider is exerting force to overcome wind resistance.)
Now that you know what balanced and unbalanced forces are and are familiar with some examples, expand your knowledge by exploring different types of forces. Start by reviewing common examples of non-contact forces. Once you have done that, move on to learning about contact forces. Chances are that you'll be really interested to learn more about the many ways force impacts people and objects all the time.