Balanced and Unbalanced Forces

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Balanced and Unbalanced Forces
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Warm-up
What allows you to peddle your bike, blow your
nose, chew gum or swim in a pool?
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Forces
So, What is a force?
A force is a push or pull Force gives an object
the energy to move, stop moving, or change
direction.
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Forces
You exert forces on other objects We would never
be able to move without exerting forces on other
things
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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
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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.

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Forces
Forces always occur in pairs Forces can be
balanced or unbalanced
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Balanced Forces
Balanced Forces DO NOT cause a change in
motion. Unbalanced forces do cause a change in
motion
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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
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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
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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
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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)

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Unbalanced Forces

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

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Unbalanced Forces
Imagine your familys 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
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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.
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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.
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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.