Balanced and unbalanced forces

Balanced and unbalanced forces

By Victoria Aertssen

​What do you already know?

​Forces can act in 6 different ways...

Multiple Choice

Forces can: change the shape of an object

• True

• False

Multiple Choice

Forces can: change the direction of an object

• True

• False

Multiple Choice

Forces can: move an object from rest

• False

• True

Multiple Choice

Forces can: stop an object

• True

• False

Multiple Choice

Forces can: speed up an object

• True

• False

Multiple Choice

Forces can: slow down an object

• False

• True

• There are at least two forces acting on all objects at rest:

  • The objects weight due to gravity (pull towards the Earth)

Normal force (push from the surface holding the object up)​

Long Answer

Yes!

​Short Answer

Do forces act on objects “at rest”?

Example: person “at rest”​

These forces are balanced (weight and normal force are equal)

The person is “at rest”.

If the chair could not balance the force of gravity she would fall through.​

Balanced forces​

For forces to be balanced then:

• The magnitude (size) of the two forces must be equal.

• The direction of the two equal forces must be opposite.

The objects motion will not change.​

Open Ended

Give an example of a balanced force that you might experience in your everyday life!

Unbalanced forces​

When one force is bigger than another the forces are unbalanced.

This will cause:

• A change in motion 

  (start, stop, speed up or slow down)

• A change in direction

• A change in shape​

Multiple Choice

Which of these is an unbalanced force?

• Resting against a wall

• Standing on the ground

• Apple falling to the ground

• Lying in bed

Start/Stop moving

Acceleration/deceleration

Change in shape/direction

​UNBALANCED

Constant speed

OR

At rest

​

BALANCED

​Example: Bike rider

Forward force from the pedalling is equal to the friction force pushing backwards.

The forces are balanced. 

The bike is travelling at a constant speed

without changing direction.

​Note the arrows are

the same length​

​Unbalanced forces

​To change the motion of the bike the rider must unbalance the forces by:

• Applying a brake force

• Applying less driving force than friction

• Applying a bigger driving force than the friction

​Note the arrows are

not the same

length​

​Buoyancy (the Archimedes Principle) 

​Buoyancy is an upward force produced by a gas or liquid.

• Buoyancy happens when an object is lighter than the gas/liquid.

Multiple Choice

What is the motion of the car?

• Drag

• Thrust

• Buoyancy

• R

Multiple Choice

What would need to change for the car to travel at a constant speed?

• Thrust decrease to equal the drag

• Thrust increase to equal the drag

• Buoyancy increases to equal upward force

• Buoyancy decreases to equal upward force

Multiple Choice

What will happen to the speed of the car if the caravan gains weight? (Adds more clothes/food/people)

• The car will go faster

• The car will stay at the same speed

• The buoyancy of the car will increase

• The car will go slower

​Net Force

​Net force is the total force acting on an object.

• Add the forces when they operate in the SAME direction.

Subtract the forces when they operate in DIFFERENT directions.

Multiple Choice

Calculate the Net force

• 7N

• 17N

• 3N

• 10N

Multiple Choice

Calculate the Net force

• 20N

• 10N

• 0N

Multiple Choice

Calculate the Net Force

• 10N

• 0N

• 15N