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Motion & Forces
Motion & Forces
Speed & VelocitySpeed & Velocity
• Speed - the rate of change in position over time (distance/time)
• Instantaneous speed
• Average speed
• How is velocity different from speed? Velocity describes both
speed and direction
Change in Velocity
Change in Velocity
What makes an object change velocity?
ForceForce• Push or Pull
• Forces can cause a change in velocity
• Examples:
GravityMagnetismFriction
Balanced ForcesBalanced Forces
Forces that– act on the same object
– are opposite in direction
– are equal in size
Balanced ForcesBalanced Forces Book on table
1. Weight of the book is downward force caused by gravity
2. Table pushes back with an equal and opposite force
Net force is zero
Unbalanced Forces
Unbalanced Forces
Forces that are NOT opposite and equal
What do they cause?
CHANGE IN VELOCITY
ACCELERATION
Forces that are NOT opposite and equal
What do they cause?
CHANGE IN VELOCITY
ACCELERATION
FrictionFrictionForce that opposes motion between 2 surfaces
Depends on the:• types of surfaces•force between the surfaces
Force that opposes motion between 2 surfaces
Depends on the:• types of surfaces•force between the surfaces
Types of FrictionTypes of Friction• Static Friction: (Couch Potato)
– Force between objects at rest
• Sliding Friction: (Ice skating)– Solid surfaces slide over each other
• Rolling Friction: (Rollerblading)– An object rolls over a surface.
• Fluid friction: (Submarine)– An object moves through a fluid
FrictionFrictionFriction is greater...
–between rough surfaces
–when there’s greater force between surfaces (such as more weight)
Friction is greater...
–between rough surfaces
–when there’s greater force between surfaces (such as more weight)
LubricantLubricant
Changes sliding friction into fluid friction
FrictionFriction
Is friction always bad?
GravityGravity
The attractive force between all objects in the universe
Acceleration of Gravity
Acceleration of Gravity
Near the surface of the earth the acceleration due to gravity is 9.8 m/s/s
Newton’s 1st Law
Newton’s 1st Law
An object at rest remains at rest and an object in motion will continue moving at a constant velocity unless acted on by unbalanced forces.
Newton’s Laws of Motion
Newton’s Laws of Motion
Newton’s 1st Law
Newton’s 1st Law
INERTIA
• tendency of an object to resist any change in its motion
• increases as mass increases
Newton‘s 2nd Law
Newton‘s 2nd Law
If more force is applied, an object will be accelerated _____more
Newton’s 2nd Law
Newton’s 2nd Law
• More force means more acceleration
• More mass means less accelerationForce = mass X acceleration
F = ma
Newton’s 3rd Law
Newton’s 3rd Law
For every action, there is an equal and opposite reaction.
Forces occur only in pairs– Act on different objects– Equal and opposite
Newton’s 3rd Law
Newton’s 3rd Law
The hammer exerts a force on the nail to the right.
The nail exerts an equal but opposite force on the hammer to the left.
Momentum
Momentum
Terminal VelocityTerminal Velocity
The final speed of a falling object.
Terminal VelocityTerminal Velocity
Air resistance is offsetting the the weight of the object
ForcesForces
EndEnd
ForceForce
Aristotle's idea:
For an object to move at a constant speed, a constant force must be applied.
ForceForce
Newton’s idea:
An object moving at a constant speed will continue at that speed without additional force being applied.
Balanced ForcesBalanced Forces