What is Galileo’s Law of Inertia?Only when friction is present is a force needed to keep an object moving.

Friction: the force resisting motion Acts between materials that touchActs in opposite direction of the motion

2

Stop and Jot Why can the student slide farther in socks

than in shoes?

Sketch a quick free body diagram of the student while he/she is sliding.

What is Newton’s First Law of Motion?An object at rest stays at rest and an object in motion stays in motion, unless acted on by an nonzero net force.

This is also known as: “The Law of Inertia”

4

What is Newton’s First Law of Motion? (continued)

No Net Force

What is Inertia?

Inertia: an object’s resistance to change its motion.

Objects want to keep doing what they do!

ACCELERATOR:

What happens to you in the car when your parents are driving

then suddenly slams on the breaks? What

do seatbelts do to keep you safe? What do you think would

happen if you did not have your seatbelt on?

Please answer this question in at least 3 complete sentences on the top of your guided

notes:

Biker Example of Newton’s First Law What happened? What does this have to do with Newton’s First

Law?Bike was in motion, and acted on by an

outside force, so it stopped.

Biker was in motion, but no force acted the biker, so he continued to go in motion (forward)

Throwing a ball in space Is there friction? Is there gravity? What happens?

It will continue to go at the same speed in the same direction forever, because there are no outside forces acting upon it

10 Minute Practice1. If a ball is in space (an area with no net

outside forces) and moving north at 3m/s, what will be its speed and direction forever? Why?

2. If a ball is rolled across a frictionless surface, will it ever slow down (refer to Newton’s First Law)?

3. If an object is at rest, according to Newton’s 1st Law, what must you do to get it moving?

4. What is friction?5. A 2kg object is moving with an acceleration

of 10m/s2. How much net force is required to keep the object moving at this speed and in this direction?