Force, Mass and Acceleration

1
Chapter 2.3 3

• Force, Mass and Acceleration
• Newtons Laws

2
Sir Isaac Newton

• An English Mathematician and Physicist that
  formulated the three laws of motion, law of
  universal gravitation and invented calculus
  before the age of 30
• Newtons discoveries helped to answer many
  questions such as what causes tides, how do the
  planets move and why do objects of different
  masses fall at the same rate?

3
What is Force?

• Force is a push, pull or any action that has the
  ability to change motion (This doesnt mean that
  a force will always make something move can you
  think of a situation such as this?)
• There are two units that are commonly used to
  measure force, Newtons and Pounds. Scientists
  prefer Newtons(N)

4
Force vs. Mass

• The Newton relates to force and motion. A force
  of 1 Newton causes a 1 kg mass to have an
  acceleration of 1 m/s2
• We call it a Newton because that is somewhat
  easier to say than 1 kg times 1 m/s2

5
Newtons First Law

• Known as the 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
Inertia

• Inertia is dependant on mass, therefore an object
  with more mass would have a greater inertia
• Example Which is harder to move, a bowling ball
  or a beach ball? The ball with the greater mass
  is harder to move because it has greater inertia

7
Newtons 2nd Law

• Relates the applied force to an objects mass and
  its 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

8
Using Newtons 2nd LawF ma
F
A
M
An objects Force equals its mass times its
acceleration
9
Balanced vs. Unbalanced Forces

• The motion of an object depends on the total of
  all forces acting on it
• If the forces are balanced, then the object is in
  equilibrium and there is no chance of movement
  occurring because the net force is zero
• If there is a net force, then the forces are
  unbalanced, and movement occurs

10
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
• A certain mass of something has a weight, which
  is the force acting on that mass. It varies
  depending on the gravity.

11
Gravity, Mass and Weight

• Imagine that you travel to the moon. Which of
  these will be the same as on earth Gravity,
  your mass or your weight?
• An object will have the same mass on the moon as
  on earth it still has the same amount of matter
• 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

12
Gravity

• The acceleration due to gravity on Earth is 9.8
  m/s2
• On earth, every kilogram of mass weighs 9.8
  Newtons
• You can figure out the weight by multiplying the
  mass times the acceleration of gravity
• F m X a

13
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
• If you drop a bowling ball and a match box car at
  the same time, they will hit the ground at the
  same time

14
Friction

• Friction is a force that resists other kinds of
  movement
• Friction always works against the movement of the
  object it comes from two objects moving against
  each other
• We use the term friction to describe any force
  caused by motion and that acts to slow motion down

15
Types of Friction

• Air friction- Air moving around objects creates
  an opposing force
• Sliding friction- Caused when two surfaces rub
  against each other
• Viscous friction- Objects that move in water or
  other fluids create this type.
• Rolling friction- Caused by one object rolling
  over another

16
Newtons Third Law

• For every action, there is an equal and opposite
  reaction
• In other words, for every object, there is a PAIR
  of forces acting on it
• 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
  tables force on you is reaction force