Forces and Newton’s Laws

What is a force in science?

In science a force is simply a push or a pull

When one object pushes or pulls another object it is exerting a force

on that other object.

Which object is exerting the force?

Is it a push or pull force?

Which object is exerting the force?Is it a push or pull force?

Which object is exerting the force?Is it a push or pull force?

Which object is exerting the force?Is it a push or pull force?

Where is the force coming from here?Is it a push or pull force?

Here is a tough one… can you figure it out?

Forces are described in two ways.

1.How strong the force is

2.What direction the force is

We illustrate forces with arrows. The

wider the arrow the stronger the force while the direction of the arrow shows the direction of the

force

If the forces are going in the same direction you add them together to

find the net or overall force

-If forces are going in the opposite direction subtract them. The bigger

force “wins” so the net or overall force will be in that direction

When you add or subtract the forces and get a net force other than zero, the object

that is being pushed or pulled will change its motion in one of three ways.

1. It might start moving or speed up

2. It might stop moving or slow down

3. It might change direction

Did that sound familiar?

It sounds familiar because speeding up, slowing down or changing direction are all examples of

changes in velocity or…

Acceleration!Anytime an unbalanced force acts on an

object it will accelerate

If the forces exactly match each other we call them balanced forces. Balanced forces

cancel each other out so there is no net force and there is no change in motion.

If the forces do not exactly match we call them unbalanced forces. These are forces that do not cancel each other out – so there

is a net force which causes a change in motion.

Go to text book page 315 and look at the three pictures of the people pushing on the boxes.1. Which two examples show unbalanced forces and why?2. Which one example shows

balanced forces and why?