1. Newton’s 1st Law
Forces and Motion

2. Today Goal: To have a basic understanding of Newton’s 1st law.
To have enough background for tomorrow’s lab which we you will identify: inertia , unbalanced forces and balanced forces.

3. Today
1st 30 minutes:
Follow along with the PowerPoint and demonstrations.
Fill in the missing words on your notes page.

4. Newton’s Laws If this book started to move, what would you think?
You’d look for a cause, or a force.

5. Aristotle 384 BC – 322 BC
Greek Philospher
Aristotle thought this was reasonable. He thought that a force had to maintain motion.
A force is a push or a pull. Anything that makes an object move, or stop moving.
BrainPop: Force

6. Example:
A cannon ball in a cannon, is at rest. The gases ignite and expand and force the ball out.
What keeps the ball moving after it leaves the cannon?
Are the gasses still working on the ball?
No. Inertia is the force that keeps it moving

7. Another example:
When you throw a baseball, what keeps the ball moving?
Is your hand still working on the ball?

8. No, inertia is what keeps objects moving
Inertia - Another word for “laziness” or the resistance of an object to change states of motion.
If an object is moving, it “wants” to stay moving.
If an object is at rest, it “wants” to stay at rest.

9. Inertia is a property of mass
Imagine trying to catch a thrown bowling ball.
Now imagine trying to catch a volleyball.
The bowling ball has more mass, and therefore has more inertia.
It takes more force to over come the inertia of the bowling ball.
Remember, mass is a measure of how much “stuff” or particles are in an object.

10. Inertia Demonstrations
Table Cloth
Bowl of Cheerios
Pen vs Pencil
You give someone a heavy pen and a light pencil and ask someone which is heavier.  They will sort of lift both of them to see.  Basically they’re measuring their “inertia” to see which is heavier

11. Newton’s 1st Law Sometimes called the Law of Inertia
An object at rest will stay at rest, and an object in motion will stay in motion unless acted upon by an outside force.
Sir Isaac Newton
English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian
Brainpop: Sir Isaac newton

12. Balanced Forces
So…According to Newton, an object will want to stay at rest or keep moving at the same speed in the same direction.
Balanced force – an object at rest, or moving at a constant velocity (same speed in the same direction), or equal forces in opposite directions.

13. Outside Forces
Unbalanced force – causes a change in motion of an object.
It can change the speed (make it go slower or faster)
It can change the direction it is moving.
It can make a resting object move.
It can make a moving object stop.

14. Unbalanced Force
Any force that changes the direction, speed or motion of an object:
A kick
A pull
A twist

15. So…. In a vacuum, like space, a baseball thrown would go on forever.
But what happens on Earth?
What is the outside force that stops the baseball?
Friction (air resistance) and Gravity

16. What is this unbalanced force that acts on an object in motion?
AND
Friction
Gravity
Air resistance is a type of friction

17. Other Outside Forces (that cause an unbalanced force)
Friction is the resistance of one surface or object rubbing against another.
From Glencoe Physical Science

18. Friction
The resistance of air on the baseball slows the ball, creating an unbalanced force.

19. Friction
Imagine if you were trying to move this box on a sheet of ice, instead.
It would be easier because there would be less friction.
From Glencoe Physical Science

20. Gravity
Gravity is a force of attraction between two objects. Earth is a large object, so it pulls other objects towards it.
Gravity also depends how close the objects are to each other. Our Earth has very little pull on Mars compared to our Moon, for example.

21. Gravity
The pull of the earth on the baseball keeps the ball for exiting the atmosphere.
It takes a lot of force to overcome gravity of large objects like Earth.

22. Outside Forces
And of course, don’t forget: Unbalanced forces Can cause a change in motion of an object.
It can change the speed (make it go slower or faster)
It can change the direction it is moving.
It can make a resting object move.
It can make a moving object stop.

23. Recap of 1st Law
Inertia is the tendency of an object to resist changes in its velocity: whether in motion or motionless.
These pumpkins will not move unless acted on by an unbalanced force.

24. Recap of 1st Law
Once airborne, unless acted on by an unbalanced force (gravity and air friction), it would never stop!

25. Recap of 1st Law
Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.

26. Newton’s 1st Law and You
According to Newton’s 1st Law, why do you think it’s important to wear seat belts?
Don’t let this be you. Wear seat belts.
Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/hour is stopped by the brick wall, your body keeps moving at 80 km/hour.