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Newtons Laws of Motion

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Title: Newtons Laws of Motion


1
Newtons Laws of Motion
  • Chapter 6

2
Causes of Motion
  • Aristotle (384-322 BC) believed that all object
    had a natural place and that the tendency of an
    object was to reside in its natural place.
  • All objects were classified into categories of
    earth, water, air, or fire.
  • Natural motion occurred when an object sought
    to return to its natural place after being
    moved from it by some type of violent motion.
  • To keep an object moving would require a force.

3
These views remained widely supported until the
1500s when Galileo Galilei (1564-1642) popularized
experimentation.
Isaac Newton (16421727) proposed that the
tendency of an object was to maintain its current
state of motion.
4
Sir Isaac Newton (1642 1727)
  • Built on Galileo, Kepler, and others
  • Worked out the three laws of motion governing
    the movement of all objects at all times an in
    all circumstances.
  • He published them in his book Philosophiae
    Naturalis Principia Mathematica (mathematic
    principles of natural philosophy) in 1687.

5
Sir Isaac Newton
  • 1st Law an object at rest or in motion stays at
    rest or
  • in motion unless acted upon by
    an outside force
  • Known as the Principle of Inertia
  • 2nd Law describes how an object accelerates or
  • changes direction when a force
    is applied to it
  • F ma
  • 3rd Law for action there is an equal and
    opposite
  • reaction

6
What is a Force?
  • Force can be defined as a push or a pull.
  • (Technically, force is something that can
    accelerate objects.)
  • Force is measured by N (Newton).
  • A force that causes an object with a mass of 1 kg
    to accelerate at 1 m/s is equivalent to 1 Newton.

1 Newton kg m/s2
7
What are the types of Forces?
8
Types of Forces
9
Contact Forces vs. Long-Range Forces
  • Contact Force acts on an object only by
    touching it. (ie. Books resting on a desk)
  • Long-Range Force forces that are exerted
    without contact or forces resulting from
    action-at-a-distance, (ie. force of gravity).
  • Types of Forces see Table 6-2 in your books!

10
Forces have Agents
  • Each force has a specific, identifiable,
    immediate cause called the agent.
  • How to solve for agents
  • 1. Create a pictorial model of situation.
  • 2. Circle the system and identify every place
    where the
  • system touches the environment.
  • 3. It is at these places that contact forces are
    exerted.
  • 4. Then identify any long-range forces on the
    system, ie.
  • Force of gravity (Fgrav).

11
Example of Forces having Agents
  • A physics book resting on a desk.

12
Newtons 1st Law of Motion
Law of Inertia
  • An object at rest tends to stay at rest and an
    object in motion tends to stay in motion with the
    same speed and in the same direction unless acted
    upon by an unbalanced force. (outside force)

The velocity of an object remains constant
unless acted on by an unbalanced force.
13
Newtons 1st Law of Motion
14
Newtons 1st Law of Motion
  • Inertia - the resistance an object has to a
    change in its state of motion. Newtons 1st Law
  • Equilibrium - if the net force on an object is
    zero, then it is said to be in equilibrium.
  • An object is in equilibrium when at rest or
    moving at constant velocity.

15
Balanced Forces
16
UnBalanced Forces
17
Some Examples from Real Life
A soccer ball is sitting at rest. It takes an
unbalanced force of a kick to change its motion.
  • 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.

18
Net Force
  • After you have added and subtracted all the
    forces you are left with the net force acting on
    the object.
  • There are several common forces acting on objects
    that you need to memorize

19
Free Body Diagrams
  • To keep track of how all these forces are
    affecting a single object, it is a good idea to
    draw a free body diagram.
  • A free body diagram is just a simple sketch of
    the object showing all the forces that are acting
    on it.
  • Draw a quick sketch of the object.
  • Draw an arrow showing every force acting on the
    object.
  • To calculate the net force, add any vectors
    acting on the same axis (x and y), making sure to
    pay attention to the directions.

20
Examples of Free Body Diagrams
21
Examples of FNet
22
Examples of FNet
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