Balanced and Unbalanced Forces

Warm-up What allows you to peddle your bike, blow your nose, chew gum or swim in a pool?

So, What is a force? Forces A force is a push or pull Force gives an object the energy to move, stop moving, or change direction.

You exert forces on other objects We would never be able to move without exerting forces on other things

A flag blows because the wind exerts a force Forces When you write with a pen you exert a force A flag blows because the wind exerts a force A magnet exerts a force on iron

Forces Two forces that are very common are: Gravity- a force that pulls all objects towards the center of the Earth. Friction – a force that resists motion between two surfaces that are in contact.

Forces Forces always occur in pairs Forces can be balanced or unbalanced

Balanced Forces DO NOT cause a change in motion. Unbalanced forces do cause a change in motion

Balanced Forces Have you ever had an arm wrestling competition? There was a probably a time when Both of you were pushing as hard as You could but your arms stayed in place

Balanced Forces The forces exerted by each person is equal, but opposite in direction So they cancel each other out and no motion takes place

Balanced Forces What would happen during a game of tug of war, if two teams exerted the same amount of force on the rope? The two forces would cancel each other out and the result would be no motion

Unbalanced Forces Unbalanced forces are not equal and this causes motion When two unbalanced forces are in opposite direction, the net force is exerted in the direction of the larger force (subtract) Net Force 15 Newtons (N) 40 Newtons (N) 25 Newtons (N)

Unbalanced Forces When two unbalanced forces are in same direction, the net force is exerted in the direction of the force (add).

Unbalanced Forces Imagine your family’s car breaks down on the road and you have to push it into a parking lot. If you push the car with a force of 25 N and your sister pushes the car with a force of 15 N It would look like this: You both are pushing in the same direction so you add the forces to get the net force 15 N and 25 N Net force = 40 N

Practice Problems Two tugboats are moving a barge. Tugboat A exerts a force of 3000 newtons (N) on the barge. Tugboat B exerts a force of 5000 newtons (N) in the same direction. 1.What is the combined force on the barge? 2. Draw arrows showing the individual and combined forces of the tugboats in #1.

Practice Problems 3. Now suppose that Tugboat A exerts a force of 2000 Newtons (N) on the barge and Tugboat B exerts a force of 4000 Newtons (N) in the opposite direction. What is the combined force on the barge? 4. Draw arrows showing the individual and combined forces of the tugboats in #3.

Practice Problems 5. Could there ever be a case when Tugboat A and Tugboat B are both exerting a force on the barge but the barge doesn't move? Draw arrows showing the individual and combined forces in such a situation.