Understanding Balanced and Unbalanced Forces: Inertia, Friction, Gravity, and Magnets, Exams of Acting

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Balanced and Unbalanced Forces

How do balanced and unbalanced forces affect an object's motion?

Inertia is the resistance of any physical object

to any change in its state of motion, including

changes to its speed and direction.

Inertia tells us the we need a force to get an

object to move or stop an object from moving.

What is inertia?

• In science, a force is a push or a pull.
• All forces have two properties:

Direction and Size

• A newton (N) is the unit that describes the

size of a force.

What is a force?

• The student is pushing down on the chair, but the chair does not move. •The floor is balancing the force by pushing on the chair.

What is a force

•When forces are applied in the same

direction, they are added to determine

the size of the net force.

Forces in the Same Direction

• When two forces act in opposite directions, you

subtract the smaller force from the larger force to determine the net force.

• The net force will be in the same direction as the larger force.

Forces in Different Directions

• When the net force on an

object is not 0 N, the forces on the object are unbalanced.

•Unbalanced forces produce a change in motion of an object.

Unbalanced Forces

350 N

Net Force ____________

Let’s Practice!

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75 N

150 N

75 N

Net Force _________________

Let’s Practice

10 N

30 N

10 N

Net Force: __________

Let’s Practice

• Friction is the force that opposes the motion between two surfaces that touch. •The surface of any object is rough. •Even an object that feels smooth is covered with tiny hills and valleys. •The contact between the hills of valleys of two surfaces causes them to stick , resulting in friction.

Friction

• The amount of friction depends on:
• Roughness of the surfaces
• Force pushing the surfaces together

Friction

Static friction occurs when force applied

to an object does not cause the object to

move.

Types of Friction

•To reduce the amount of friction, apply a

lubricant between two surfaces.

Ex) Motor oil, wax, and grease

•Friction can also be reduced by rolling ,

rather than pushing , an object.

Reducing Friction