Forces And Motion

Forces and Motion

Motion Motion is an object’s change in position relative to a reference point or frame of reference.

Speed and Velocity 

Speed describes how fast an object is moving • Average speed = Distance / Time

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Velocity is speed and direction • V = d/t

What is the velocity of a swimmer who swims 110meters towards the shore in 72 seconds? • V = 110 / 72 = 1.5 m/s towards the shore

Acceleration Acceleration is the rate at which velocity changes over time. It’s a change of speed or direction. Acceleration = Final V – Initial V time Jim accelerates his skateboard along a straight line from 8 m/s to 16 m/s in 3 seconds. What was his average acceleration? a = 16 – 8 = 8 =2.66 m/s2 along a line 3 3

Force A

force is anything that changes the state of rest or motion of an object.

 Balanced

forces do not cause a change in motion. An object will begin to accelerate if the forces are unbalanced.

Friction  Friction

is the force that opposes motion between two surfaces that are in contact.  Static Friction – friction between surfaces that are not moving.  Kinetic Friction – friction between moving surfaces.

Reducing Friction 

Oil, wax, grease

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Ball bearings – replacing sliding friction with rolling friction

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Make surfaces smoother.

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Streamlining – reduces friction with air/water

Increasing Friction  Make

surfaces rougher

 Increase

force pushing objects together

Forces – Laws of Motion st Newton’s 1 Law 

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“An object at rest or in motion will remain at rest or in motion unless acted upon by an outside force.” Often, this outside force for an object in motion is friction and/or gravity. For an object at rest, the force is often a push or pull Inertia is the tendency for an object at rest to remain at rest or an object in motion to remain in motion. Matter resists any change in motion

Forces – Laws of Motion nd Newton’s 2 Law 

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The acceleration of an object is directly proportional to the force exerted on it and inversely proportional to its mass. The harder you push on an object the faster it will accelerate. The smaller the mass the faster an object will accelerate. Force is measured in NEWTONS (N) Force = mass x acceleration F = ma

Forces – Laws of Motion rd Newton’s 3 Law  For

every action force there is an equal and opposite reaction force.  All forces act in pairs!!

Gravity  

Gravity is the force of attraction between any two objects How strong gravity is depends on: – Mass of the objects – the gravititational force is large when one or both objects have large masses. Every piece of matter exerts a gravititational force. – Distance between two objects – the greater the distance, the less the gravititational force

Mass and Weight  Mass

is the amount of matter in an object (grams)

 Weight

is the measure of the pull of gravity (Newton)

Free Fall  Free

fall occurs when gravity is the only force acting on an object. When an object is dropped on earth its velocity will increase until the force of air is equal to gravity (called terminal velocity)