1. What do you think the natural state of an object is. Motion. Rest
What do you think the natural state of an object is? Motion? Rest? Something else?

2. MOTION: REST: SOMETHING ELSE:
Class Opinion:
MOTION: REST: SOMETHING ELSE:

3. Why does a bullet stop?
Why might a hockey puck not move as well on gravel as it does on ice?
What do you think would happen if you threw a baseball, and neither gravity nor air resistance acted upon it?

4. Aristotle’s Thoughts on Motion
Natural Motion
Not caused by forces
Straight up or down. Light things rise, heavy things fall.
Objects seek their natural
resting place.
Circular motion is natural
for the heavens
Falling Boulder ground
Rising Smoke air

5. Violent Motion Push or Pull Imposed Motion
Has an external cause. Objects could not move on their own.

6. Copernicus (1473-1543) The easiest way to explain astronomical
observations was to
assume that the Earth
was moving.
The planets revolved around the sun…
WHAAAAT?!

7. Galileo Galilei On house arrest for believing Copernicus
Demolished the idea that a force is necessary to keep an object moving

8. What do you think?
Force
Friction
Examples

9. Galileo’s thoughts Force- any push or pull
Friction- the name given to the force that acts between objects that touch as they move past each other.
Force is only needed to keep an object moving when friction is present
Without friction, a moving object would maintain a constant speed forever!!
Every material object resists change to its state of motion…

10. Aristotle was way off!
It was not the nature of the ball to come to rest. It was friction.
A moving ball would prefer to keep moving naturally.
The reluctance of any body to change its state of motion is called inertia.

11. Things tend to do what they are already doing!
The Law of Inertia
Every object continues in a state of rest, or of motion in a straight line at constant speed, unless it is compelled to change that state by forces acted upon it.
Things tend to do what they are already doing!

12. Newton’s 1st Law of Motion

13. Mass
Inertia
Weight

14. Inertia Vs. Mass
Inertia is the tendency of an object to resist changes in motion.
Mass is the amount of matter in an object.
Mass depends only on the amount and kinds of atoms in an object.
Mass is measured in grams or kilograms.
Mass is a measure of inertia.
More mass means more resistance to changes in motion.

15. Weight vs. Mass Weight is the force of gravity on an object.
Weight depends on location.
Weight is measured in Newtons just like any other force.
A 1 kg Mass weighs 9.8 N or 2.2 lbs on Earth.

16. A Mathematical Relation
Weight and mass are related by the following equation:
Remember, we represent gravitational acceleration with a lower-case g.