1. Force, Mass and Acceleration Newton’s Laws
Chapter 3
Force, Mass and Acceleration
Newton’s Laws

2. Sir Isaac Newton 1642-1727 English Mathematician and Physicist
Formulated the three laws of motion and law of universal gravitation
Invented calculus
All before the age of 30
Newton’s discoveries helped scientists understand ideas such as: what causes tides, how do the planets move and why do objects of different masses fall at the same rate?

3. A Newton
Newton came up with a formula to help scientists understand force.
Force is measured in Kg.m/s2 this is called a Newton (named after guess who? – Newton)
There are 4.48 N in 1 lb

4. What is Force?
Force is a push, pull or any action that has the ability to change motion
Will a force always cause motion?
There are two units that are commonly used to measure force, Newtons and Pounds. Scientists prefer Newtons(N)

5. Newton’s First Law Law of Inertia
“An object at rest will stay at rest until acted upon by an unbalanced force, an object in motion will continue with constant speed and direction until acted upon by an unbalanced force”
Basically – An object at rest remains at rest and an object in motion remains in motion unless acted on by an unbalanced force.

6. Newton’s 1st Law

7. Inertia
Objects ability to resist changing its state of motion (Keep on doing what it is doing)
Inertia depends on mass, so an object with more mass would have a more inertia

8. Inertia
Which is harder to move, a bowling ball or a beach ball?

9. Newton’s 2nd Law Relates force to an object’s mass and acceleration
It says that force causes acceleration, mass resists acceleration and the acceleration is a ratio of force over mass
Common sense: If something has more mass, it would take more force to cause the object to accelerate

10. Newton’s 2nd Law
F = ma

11. Using Newton’s 2nd Law F = ma
An object’s Force equals its mass times its acceleration

12. 2nd Law
A car engine produces a force and you can calculate the acceleration of the car when you know this force and the mass of the car
If you want to increase the acceleration of the car you must decrease the cars mass or increase the force of the engine

13. Balanced vs. Unbalanced Forces
Net Force – the sum of all forces acting on an object
The motion of an object depends on the total of all forces acting on it
If the forces are balanced(net force =0), then the object is in equilibrium and there is no chance of movement occurring because the net force is zero

14. Balanced Forces
If the forces are balanced(net force =0), then the object is in equilibrium and there is no chance of movement occurring because the net force is zero

15. Unbalanced Forces
If there is a net force, then the forces are unbalanced, and movement occurs

16. Weight vs. Mass
Mass is the amount of matter in an object, usually measured in kilograms
Weight is the force of gravity acting on a certain mass, measured in Newtons or pounds
Weight changes with gravity
Mass is the same everywhere

17. Gravity, Mass and Weight
An object weighs less on the moon but has the same mass. It weighs less because there is less gravity.
You would weigh more on Jupiter than Earth because Jupiter has more gravity than Earth

18. Gravity A force that pulls every mass toward another mass
Earth is the biggest mass for us so other masses are pulled toward earth’s center
On earth, every kilogram of mass weighs 9.8 Newtons

19. Weight is a force
You can figure out the weight by multiplying the mass times the acceleration of gravity
F= m X a
Weight is a force (pulled to earth’s center)
The acceleration due to gravity on Earth is 9.8 m/s2

20. Gravity, Cont.
On Earth, every object will fall at the same rate (not counting air friction)
The Acceleration of gravity is 9.8 m/s2 meaning that every second, a falling object accelerates 9.8 m/s
In other words, every second something is falling it is moving 9.8 m/s faster

22. Gravity with no resistance
If you drop a bowling ball and a match box car at the same time, they will hit the ground at the same time

23. Newton’s Third Law
“For every action, there is an equal and opposite reaction”
There must be a PAIR of objects
The action and reaction act on separate objects

24. Newton’s Third Law
If you press down on the table, you are exerting a force on it. Is the table exerting a force on your hand?
Your force on the table is action force, the table’s force on you is reaction force

25. 3rd Law
Skateboard – foot on ground is action – earth against skateboard is reaction
Throw ball on a skateboard
Recoil – backward acceleration from reaction force

26. Law of Universal Gravitation
The force of attraction (gravity) between 2 objects depends on the mass of the object and the distance between them
More noticable between large objects (plants and stars)
Force = G x mass 1 x mass 2 d2
G = 6.67 x 10-11

27. Friction Forces that work against the motion of the object
Force of friction is always in the opposite direction of the motion
Must consider when finding net force
Will cause motion to stop eventually unless force is continually supplied

28. Air Friction
Caused by air moving around objects

29. Sliding Friction
Two objects sliding against one another

30. Rolling Friction
One object rolling over another object

31. Viscous Friction
Object moving in water or fluid