Balanced and Unbalanced Forces

What is a force?

• A force is a push or pull that causes an object to move, stop, or change direction

• Has a size and a direction

• In physics a force is anything that makes an object accelerate (remember: acceleration in science can mean speed up, slow down, change direction or change speed & direction!)

How do we measure force?

• The spring scale is the instrument used to measure force.

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• The units of measurement for force are newtons (N). Who is it named in honor of?

Mass Vs. Weight • Mass is the amount of matter in an object.

• The tool we use to measure mass is the Triple beam balance.

• The units used to measure mass are grams (g).

• Weight is the measure of gravitational force on an object.

• We measure weight with a spring scale.

• Since weight is a measure of 1 type of force,

the unit for weight in science is the newton.

Balanced and Unbalanced Forces

• Forces occur in pairs and they can be either balanced or unbalanced.

Balanced Forces

• Balanced forces do not cause change in motion

• They are equal in size and opposite in direction

Examples of Balanced Forces

Unbalanced Forces

• Unbalanced forces are NOT equal in size. • An unbalanced force always causes a

change in motion! This can be a change in speed, direction or both.

• When unbalanced forces act in opposite

directions you can find the net force. To find the net force, you

• Calculate the Magnitude of the force. This is the

difference between the two forces, so you subtract the smaller force from the larger one.

• Determine the direction of the net force. The direction

of the largest force is the direction of the force (IF they are going in opposite).

Examples of Unbalanced Forces

Unbalanced Forces

6 N, left – 3 N, right = 3N, left

Unbalanced Forces

10 N, right – 4 N, left = 6N, right

Unbalanced Forces

5 N, right + 10 N, right = 15N, right

Balanced or Unbalanced Forces?

Types of Forces

• Gravitational Force (Gravity) – is the force of attraction between objects due to their masses.

• Friction – the force that exists when there is contact between 2 surfaces (It opposes motion)

• Applied force – force that is applied to an object by a person or another object.

Types of Forces (continued)

• Net force – the combined effect of all forces acting on an object.

• Balanced – Forces are balanced when they act on an object in opposite directions and are equal in size (no change in the position, speed, or direction of motion of the object).

• Unbalanced – opposing forces that are not equal (causes change in position, direction, or speed).