forces and the laws of motion
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Forces and the Laws of Motion. Forces. Force is a push or pull on an object. Unit for force: N or Newton. Balanced forces Where there are two forces that counteract each other and result in no movement (EQUAL) Unbalanced forces One force is greater than the other force. (UNEQUAL).

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Presentation Transcript
  • Force is a push or pull on an object.
  • Unit for force:

N or Newton.

Balanced forces Where there are two forces that counteract each other and result in no movement (EQUAL)
  • Unbalanced forces

One force is greater than the other force.


  • A force that resists motion and can cause heat
  • Lubricants help reduce friction
  • Types of friction
    • Sliding
    • Rolling
    • Fluid
    • Static
Types of friction
  • Static
  • acts on objects that are not moving
  • Always acts in opposite direction to applied force
  • Sliding
  • Opposes direction of motion as an object slides
  • Less then static friction
  • Rolling
  • Friction that acts on rolling objects
  • 100 to 1000 times less than static and sliding friction
  • Fluid
  • Opposes the motion of an object through a fluid
  • Fluids include gases and liquids
  • Air resistance – fluid friction acting on an object moving
  • through the air
newton s laws of motion
Newton’s Laws of Motion
  • 1st Law: Objects at rest remain at rest, or objects in motion remain in motion unless acted upon by a force. (unbalanced)
  • 2nd Law: The acceleration of a body depends on the ratio of the acting force to the mass of the body. (unbalanced)
          • F = m x a
  • 3rd Law: for every action there is an equal and opposite reaction. (balanced)
1 st law of motion law of inertia
1st Law of Motion (Law of Inertia)
  • Inertia: force that is resistant to the direction of the motion
    • The forces are Unbalanced
  • Examples: Inertia belts (seat belts)
2 nd law of motion
2nd Law of Motion
  • Concept: Acceleration
    • The forces are unbalanced
  • Examples: hitting a golf ball gently vs. hard.
  • F = ma

Answer = _50__ newtons

Problem 1

How much force is needed to accelerate a

500.0 kg car at a rate of 4 000 m/s/s?

Problem 2

A 100 N force causes an object to accelerate at

2 m/s/s. What is the mass of the object?

Problem 3

A 1.5 kg ball is kicked with a force of 450 N.

What acceleration did the ball receive?

3 rd law of motion action reaction
3rd Law of MotionAction/ Reaction
  • Concept: Action/Reaction of objects
    • Forces are balanced
  • Examples: Stationary objects, rockets being launched
laws of motion interactives

Laws of motion Interactives



Motion of a falling object after being

given an initial forward velocity

Combination of initial vertical force

and downward force of gravity

Causes object to follow a curved path

gravity and free falling objects
Gravity and Free Falling Objects
  • Gravity: The attraction between two objects.
  • All objects fall at a rate of 9.8 m/s2
  • Gravity acts betweentwo masses
  • All masses exert the force of gravity – universal force
  • Galileo did an experiment at the leaning tower of Pisa in Italy with bowling balls. Both balls fell at the same rate.
air resistance
Air Resistance
  • Force that slows down falling objects due to the atmosphere and surface area of the object.
newton s law of universal gravitation
Newton’s Law of Universal Gravitation
  • Shows that objects are attracted to one another in proportion to their masses and their distances away from the object.
feather vs rock
Feather vs. Rock
  • Earth: feather would float down (air resistance) while the rock would drop at 9.8 m/s/s
  • Moon: feather and rock would drop at same rate due to no atmosphere and air resistance.
what about a vacuum
What about a vacuum?
  • vac·u·um[ vákyooəm ]
  • space empty of matter: a space completely empty of matter but not achievable in practice on Earth
  • space with all gas removed: a space from which all air or gas has been extracted
  • emptiness caused by absence: an emptiness caused by somebody or something's absence or removal
  • Both fall at the same rate due to there being no air.
Gravity and Weight



Mass – measure of amount of inertia

Weight – force of gravity pulling on an object

Weight is product of mass and acceleration due to gravity ( 9.8 m/s/s)

W = mg

W- weight in newtons

m- mass in kilograms

g- acceleration due to gravity in meters per second squared