1. Force, Gravity and Newton’s Laws
Vocabulary
Gravity: The fundamental force of attraction that all objects with mass have for each other
Force: A push or pull that causes something to change its motion
Friction: A force that occurs when two things move past each other and rub together

2. Isaac Newton & Force Identification

3. Sir Isaac Newton
Acclaimed as one of the foremost scientific intellects of all time.
Credited with works in Mechanics, Astronomy, Philosophy, Mathematics, Optics & Theology

4. Sir Isaac Newton Principia Philosophiæ Naturalis Principia Mathematica
"Mathematical Principles of Natural Philosophy” published in 1687
In this work, Newton described universal gravitation & 3 Laws of Motion

5. Newton’s Tomb in Westminster Abbey
What is a Force?
Newton’s Tomb in Westminster Abbey
Push or pull that acts on an object
Can cause:
A resting object to move
Acceleration
Changes in speed & direction
New Unit! Guess what it is?
Newton (N)

6. But first… the scientists who came before…
Newton wasn’t the first person to come up with this idea…
Aristotle ( B.C.) started the conversation with the proposal that force is required to keep an object moving
However, his concept was proven incorrect…

7. Galileo Galileo (1564-1642) was next…
Concluded that moving objects not subjected to friction or other forces would continue to move indefinitely

8. Descartes
Descartes ( ) was certainly on Newton’s list of study.
Published "Principles of Philosophy”
"that each thing, as far as is in its power, always remains in the same state; and that consequently, when it is once moved, it always continues to move."

9. Identifying Forces Friction
A force that opposes motion of objects “in contact” as they pass each other
“In contact” means solid objects touching or objects moving through liquid/gas
4 types: Static, Sliding, Rolling, Fluid (Air resistance)

10. Identifying Forces Gravity Force that acts between any two masses
An attractive force that pulls objects together
Does not have to be in contact!
Causes objects to accelerate (9.8 m/s2, remember?)

11. Combining Forces Force is a vector! What does that mean again?
Net force – overall force on an object after all the forces are combined
Balanced force – net force of zero, which causes no change in motion
Unbalanced forces – the net force is not zero causing object to accelerate

12. Recap What are the 3 things a force can cause?
Gravity is a(n) _______________ force that pulls ________ two objects together.
How do balanced and unbalanced forces affect the motion of an object?

13. Newton’s First Law Vocabulary
Newton’s Laws: Three laws that explain the motion of objects caused by forces
Inertia: The tendency of objects to keep on doing what they are already doing (moving or staying at rest
Momentum: The product of an object’s mass and its velocity

14. Newton’s 1st Law & Momentum
Introductory Video for First Law!

15. Newton’s 1st Law of Motion
The state of motion of an object does not change as long as the net force is zero
Known as the Law of Inertia
What is inertia?
The tendency of an object to resist a change in motion!

16. Newton’s First Law
Let’s summarize…
An object moving wants to remain in motion with the same speed and direction
An object at rest wants to stay at rest
Things want to keep doing what they are already doing!
IF THE NET FORCE ON AN OBJECT IS ZERO, THE MOITON OF THE OBJECT DOES NOT CHANGE!

17. Balanced versus Unbalanced Forces
Balanced forces cause NO change in an object’s velocity!
Unbalanced forces acting on an object cause the object to start moving!

18. Momentum Mass on the move. Product of mass and velocity.
An object with a large momentum is hard to stop
ρ = mv
ρ -momentum (kg m/s)
Bill Nye Video Clip….Momentum!

19. Recap
Who were Isaac Newton’s predecessors that influenced his first law?
Summarize what inertia means.
What would have more momentum, a soccer ball or a bowling ball? Why?

20. Newton’s Second Law Vocabulary
Mass: How much matter there is in an object
Weight: The force of gravity acting on an object

21. Newton’s 2nd Law
Introductory Video to Newton’s 2nd Law

22. Newton’s 2nd Law
A net force acting on an object causes the object to accelerate in the direction of the force
The acceleration determined by two factors.
Size of the force.
Mass of the object.

23. Don’t you already know this?
Heavier (more massive) objects require more force
to move…Ouch… the same distance.

24. Some additional summaries:
Object accelerates in the direction you apply the force.
Acceleration is directly proportional to the force. (What does that mean?)
Acceleration is inversely proportional to the mass. (What about this one?)

25. Newton’s 3rd Law
Introductory Video for Newton’s 3rd Law

26. Newton’s 3rd Law
Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force
Known as Action-Reaction forces

27. Be careful of misconceptions…
Action – Reaction forces do not necessarily cancel
Why?
The forces do not act on the same object!
Swimmer’s force is acting on the water.
What about the water?

28. Let’s try some. Press your hands on the edge of your desk.
Describe the skin around where the contact is being made.
Is it different if you weren’t pushing on the desk?
Why does your hand that presses on the desk look more distorted?
The desk is pushing on you!
Anything you can feel is something pushing on you.

29. Newton’s 3rd Law & Review Video
Stops at about 4 minutes.

30. Recap What does Newton’s 3rd law State?
Explain why the forces do not necessarily cancel.
Explain how letting the air out of a balloon could describe Newton’s 3rd law.

31. There is an equation! F = ma F – force m – mass a – acceleration
What are the units?
Remember Newton?
Try some!

32. Weight vs. Mass Remember the definitions? Mass – amount of matter
Weight – force of gravity
Notice that weight is a force?
W = mg
Let’s compare this to F=ma

33. Recap Describe how F = ma accurately explains Newton’s 2nd Law.
Provide an example of Newton’s 2nd Law in your everyday life.
How is mass different from weight?