1. Agenda for 4/21/14 Welcome back  Inertia Lab – go outside
HW – Finish lab

2. Agenda for 4/21/16 Quizzes handed back tomorrow
Newton’s 1st Law of Motion Notes
HW – Acc/Dec, Newton’s 1st Law Worksheet

3. Newton’s First Law of Motion
Unit 7 - Motion
Newton’s First Law of Motion

4. What is a force? Force - PUSH or PULL that can start,
stop or change the direction
of an objects’ motion.

5. A spring scale is used to measure force.

6. Units for force Measured in _______________ Answer: Newtons (N)
What are some forces acting on you right now?
Gravity
Air Pressure
Friction

7. Balanced Forces and Unbalanced Forces
Balanced Forces: Forces that are EQUAL in size but OPPOSITE in direction. NO Motion!

8. Balanced Forces and Unbalanced Forces
Unbalanced Forces: Forces that are UNEQUAL in size. Motion!

9. Newton’s First Law of Motion
Sir Isaac Newton stated:
“An object at rest will remain at rest AND an object in motion will remain in motion, until an unbalanced force (gravity, friction, wind resistance) is acted upon it”.
Also known as  LAW OF INERTIA

10. What does this mean?
Basically, an object will “keep doing what it was doing” unless acted on by an unbalanced force.
If the object was sitting still, it will remain stationary. If it was moving at a constant velocity, it will keep moving.
It takes force to change the motion of an object.

11. Some Examples from Real Life
A soccer ball is sitting at rest. It takes an unbalanced force of a kick to change its motion.

12. Two teams are playing tug of war
Two teams are playing tug of war. They are both exerting equal force on the rope in opposite directions. This balanced force results in no change of motion.

13. Newton’s First Law is also called the Law of Inertia
Inertia: the tendency of an object to resist changes in its state of motion
The First Law states that all objects have inertia. The more mass an object has, the more inertia it has (and the harder it is to change its motion).

15. 1st Law
Once airborne, unless acted on by an unbalanced force (gravity and air – fluid friction), it would never stop!

16. 1st Law
Unless acted upon by an unbalanced force, this golf ball would sit on the tee forever.

17. Why then, do we observe every day objects in motion slowing down and becoming motionless seemingly without an outside force?
It’s a force we sometimes cannot see – friction.

18. Friction Definition: Force that occurs when 2 substances rub together.

19. Friction! There are 3 main types of friction:
Sliding friction: friction occurring by sliding motion. ex. ice skating
Fluid friction: friction occurring through air or liquid. ex. sky diving
Rolling: friction occurring by rolling motion. ex. bowling

20. In outer space, away from gravity and any sources of friction, a rocket ship launched with a certain speed and direction would keep going in that same direction and at that same speed forever.

21. Newtons’s 1st Law and You
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 m/hour.

22. Centripetal Force
Centripetal Force - force that pushes or pulls an object into a circular path.
Always directed towards center of the circular path.

23. Examples of Centripetal Force
Swinging a piece of rope.
Ferris Wheel, merry-go-round, tilt-a-whirl.
London Ferris Wheel