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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  • 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