FORCE

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FORCE MOTION

• UNIT 2

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Motion

• Objects move in a variety of ways!
• How do we know when an object is moving?
• Constant motion - an object covering equal
  distances in equal amounts of time constant
  speed
• Non-constant motion - an object doesnt cover
  equal distances in equal intervals of time
• An object is moving if its position changes does
  the background change?
• Speed describes how fast an object moves.

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What is Speed?

• Speed measures motion.
• To determine speed you must
• Measure the distance traveled by an object
• Measure the time it takes to travel that distance

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Determining Speed?

• Dont forget to use International Scientific
  Units or SI units!
• How fast an object moves in meters per second
  (m/s) rate of motion.
• A change in position from one place to another in
  any direction is described as motion. (meters or
  kilometers)
• The length of time that it takes for that change
  to occur, or the rate of change in position is
  described as speed. (seconds or hours)

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Types of Speed

• Average speed distance covered by an object
  divided by the time it takes to travel that
  distance
• Instantaneous speed speed measured at any given
  instant
• Constant speed when speed doesnt vary over a
  long period of time
• Negative acceleration slowing down
• Positive acceleration speeding up
• Resting objects - speed of 0 m/s

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Speed Velocity

• SPEED how fast an object moves
• VELOCITY describes both speed and direction
• d
• s t
• Speed d/t
• Define and practice and more Velocity practice

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Velocity example
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Velocity example
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Momentum

• Moving objects have momentum
• Momentum depends on both its velocity and its
  mass
• Momentum has direction an objects momentum is in
  the same direction as its velocity
• If a train and a car are moving at the same
  velocity, which one has the greater momentum?

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Measuring Momentum

• The more mass an object has, the greater its
  momentum (for a given velocity)
• The faster an object is moving, the greater its
  momentum
• Momentum is zero if an object isnt moving
• SI unit is kilograms times meters per second
  (kgm/s)

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Momentum Equation

• For momentum
• momentum mass x velocity
• p mv
• p
• m v

Definition Youtube spaceship battle (Cant see at
school)
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Momentum example
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Momentum example
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Momentum example
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Acceleration

• The rate at which velocity changes not speed!
• When an object speeds up then acceleration is in
  the same direction as velocity. When an object
  slows then acceleration is in the opposite
  direction as that of velocity.

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Car acceleration

• Press on the gas car speeds up acceleration
  is in the direction of the cars motion
• Press on the brake car slows down
  acceleration is opposite to the cars direction
• Turn the steering wheel changes velocity even
  if speed doesnt change acceleration changes

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Acceleration formula

• Acceleration
• change in velocity/time
• v
• a t
• Change in velocity final velocity initial
  velocity
• v vF - vI

a v/t
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Acceleration example
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Practice

• Acceleration definition and practice
• Line Rider 2
• Definition from Physics Textbook
• Notes and practice

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Force

• A force can most easily be described as a push or
  a pull. When a force is applied to an object, the
  velocity of that object changes. This change in
  velocity constitutes an acceleration. So, forces
  are tied to accelerations.

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Force

• Net force combination of all of the forces
  acting on an object, determines whether the
  velocity of the object will change
• An object accelerates in the direction of the net
  force kicking a ball
• Balanced forces completely cancel each other and
  the combined force equals zero tug-of-war where
  rope doesnt move
• Force and Motion Experiments
• Force f
• mass acceleration m a

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Force - Balanced

• Forces on an object that are equal in size and
  opposite in direction are balanced forces and
  will not change the velocity of an object

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Force - Unbalanced

• When the forces become unbalanced the NET FORCE
  applied to the object will always change the
  velocity of the object by changing its speed or
  direction.

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Friction

• Friction is a force that opposes motion between
  two surfaces that touch.
• The amount of friction depends on the kinds of
  surfaces and the forces pressing the surfaces
  together.

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Friction

• If a ball is rolling across the floor, it will
  slow and stop. Force keeps the ball rolling and
  FRICTION is the unbalanced force acting against
  the balls direction of motion.
• Friction affects non-moving objects. Friction of
  brakes balances the force of gravity and stops a
  parked truck from rolling down a hill.
• Try walking on ice and on grass. You slip on ice
  because there is less friction between your shoes
  and the ground.

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Friction (rolling, sliding,fluid)

• Sliding friction is the strongest motion
  friction. Ex push a box across the floor.
• Rolling is used to reduce sliding friction. Ex
  wheels
• Fluid friction is from fluid or gas. It reduces
  air resistance. Oil reduces sliding friction.
  Ex WD40 on a door hinge

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Air resistance

• Another type of friction
• The amount of air resistance on an object depends
  on its size and shape as well as on the speed
  with which it moves.
• Objects with larger surfaces have greater air
  resistance. Air resistance also increases as the
  objects speed increases.

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Gravity

• Gravity is a force. Every object in the Universe
  exerts a force of gravity on every other object.
• The amount of gravity depends on mass and
  distance. The more mass an object has and the
  closer the distance to another object the more
  gravitational force.
• Gravity website and games

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Gravity Example
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Weight

• The measure of the force of gravity on an object
  is the objects weight. Weight refers to
  gravitational force between earth and a body at
  Earths surface. If a person weighs 100 pounds
  the Earths gravity is exerting 100 pounds of
  force on that person. The moon has a weaker
  gravitational force than the Earth because it
  doesnt have the mass of the Earth.

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Weight formula

• Weight mass gravity
• Gravity 9.8 m/s2
• Weight is measured in Newtons
• w
• m g

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Free fall

• Caused by gravity
• Objects experience air resistance which is fluid
  friction
• Acceleration due to gravity is 9.8 m/s2

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Newtons Three Laws
Cool website

• 1st Law -An object at rest will remain at rest
  unless acted on by an unbalanced force. An object
  in motion continues in motion with the same speed
  and in the same direction unless acted upon by an
  unbalanced force. This law is often called "the
  law of inertia".
• 2nd Law -Acceleration is produced when a force
  acts on a mass. The greater the mass (of the
  object being accelerated) the greater the amount
  of force needed (to accelerate the object).
• 3rd Law -For every action there is an equal and
  opposite re-action.

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Remember the Laws?

• 1st Law 2nd Law 3rd Law

Demonstration
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Newtons Laws of Motion

• Definition
• Simplified
• NASA site to visit
• Explanation
• Demonstrations
• Detailed information

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