Forces and Motion

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Forces and Motion
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Note taking sheet

• 1. Reference point or frame of reference p.9
• 2. Total distance p. 11
• Total time
• 3. speeding up, slowing down or changing
  direction p. 14-15

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• 4. an objects resistance to a change in motion p.
  19
• 5. as velocity increase momentum increase
• p. 20

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Motion

• What do you think it means to be in motion? How
  can we tell if something is in motion?

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Motion

• Motion a change in position, measured by
  distance and time. 

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Motion

• Determining if an object changes position
  requires a frame of reference.
• The Earth is the most common frame of reference

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Speed

• Speed the distance traveled by a moving object
  per unit of time
• To calculate speed, use the equation
• Speed distance / time
• Speed only gives distance and time!

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Average Speed

• Average speed the speed of moving objects is not
  always constant
• To calculate average speed you look at total time
  and distance

Average speed total distance / total time
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Average Speed

• 1. What is your average speed if you take 2h to
  jog 8 miles ?
• Speed distance/ time
• 8m/2h 4 mph
• 2. What is the average speed of a car if it
  travels 500 miles in 20 hours?
• Speed distance/ time
• 500m/20h 25 mph

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Velocity

• Velocity is speed in a given direction.
• Velocity gives distance, time, and the direction
  of travel.
• Velocity changes by changing direction or
  changing speed!

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Scientists have a special way to measure a change
in velocity

• Acceleration

Acceleration is a change in velocity.
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Acceleration

• The change in velocity divided by the time it
  takes for the change to occur
• Acceleration
• (final velocity initial velocity)
• time
• Velocity is measured in m/s and time in seconds.
• Units for Acceleration are m/s/s

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Calculating Acceleration

• A roller coasters velocity at the top of the
  hill is 10 m/s(initial) Two seconds later its
  velocity is 26 m/s (final). What is the
  acceleration of a roller coaster?
• Acceleration final velocity- initial velocity
• time
• Accel 26m/s -10m/s 16 8 m/s/s
• 2 s 2 s

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The Way Acceleration Works

• If youre speeding up, you have positive
  acceleration.
• If youre slowing down, you have negative
  acceleration.
• If youre changing speed quickly, you have high
  acceleration.
• If youre changing speed slowly, you have low
  acceleration.

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True or false?

1. If you slow down on your bicycle, you accelerate.
2. If you ride your bicycle at a constant speed, you
   cannot accelerate
3. Changing the speed and changing the direction of
   your bicycle are both examples of acceleration.

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Example

• Youre driving along in your car and suddenly
  have to slam on your brakes for a red light.
  Negative or positive acceleration? High or low
  acceleration?

High negative acceleration because youre slowing
down quickly.
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Momentum

• Momentum
• The measure of how difficult it is to stop a
  moving object

p mv
p momentum (kg m/s) m mass (kg) v velocity
(m/s)
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Calculating Momentum

• A 20,000 kg ship is traveling east at 20 m/s.
  What is the momentum of the ship?
• Pmv
• 20,000 kg X 20 m/s
• 400,000 kg m/s

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Law of conservation of momentum

• According to the law of conservation of momentum
  the total momentum of objects that collide will
  be the same before and after the collision.
• Momentum will not be lost during the collision.

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Quick Review

• Velocity speed of motion
• Acceleration change in velocity
• Momentum The measure of how difficult it is to
  stop a moving object

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Calvin and Hobbes

• S D/T
• 50 yd/ 10 min
• 5 yd/min

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Force

• Force any push or pull

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• Forces are measured in _____
• A _____ is the combination of all of the forces
  acting on an object.

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Forces
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Force

• Balanced Forces

• forces acting on an object that are opposite in
  direction and equal in size
• no change in velocity

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Balanced vs. Unbalanced Forces

• Balanced forces will not cause a change in the
  motion of an object they have a net force of
  zero N.
• Examples of balanced forces are
• 1. ______, 2. _____, 3. _____ .

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Balanced vs. Unbalanced forces

• Unbalanced forces could be best described as
  __________________________ .
• Examples of unbalanced forces are
  ___________________________ .

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Force Drawing

• Create a drawing that shows an example of
  balanced forces. The drawing should show the
  forces acting on the object and what happens to
  the object if the forces become unbalanced.

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Forces
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Forces

• You and a younger brother or sister are at a
  neighborhood pool. Your brother or sister asks
  why there are signs that say NO RUNNING! What
  would be your answer?

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Forces

• _____ , ______ , and ______ are examples of
  common lubricants.
• Therefore, it is easier to slip when there is
  water on the floor because the water acts as a
  ______ that lessens the friction between the
  bottom of your shoe and the floor.

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Pushing pedals, pressing brakes, and kicking
soccer balls are all examples of forces.

• A force is anything that changes the velocity of
  an object.
• But whats a change in velocity?
• A change in velocity is acceleration, so . . .
• A force is anything that gives an object
  acceleration.

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Friction

• _____ is a force that opposes motion between two
  surfaces that are in contact.
• A _____ is a substance that lessens friction.

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Friction

• Friction
• force that opposes motion between 2 surfaces
• depends on the
• types of surfaces
• force between the surfaces
• A _____ is a substance
• that lessens friction.

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Friction

• There are four types of friction.

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Friction

• Four Types of Friction
• Static Friction force that acts on objects that
  are not moving. (Couch Potato)
• Sliding Friction - force that opposes the
  direction of motion of an object as it slides
  over a surface. (Ice skating or bobsledding)
• Rolling Friction friction force that acts on
  rolling objects. (Rollerblading)
• Fluid Friction force that opposes the motion of
  an object through a fluid. (Planes flying or
  submarines traveling)

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Friction

• Write a story that describes what a day in your
  life would be like if there was no friction.

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• Gravity

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Gravity

• Isaac Newton discovered the ______ ______ of
  Gravitation.
• Gravity acts on any objects with mass.
• Example You and your books, pencils, paper, etc.

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Universal Law of Gravitation

• Mass and gravity have a directly proportional
  relationship.
• The distance between the centers of masses of the
  two objects and gravity have an inversely
  proportional relationship.

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Differentiate between Mass and Weight.

• Weight is dependent upon the acceleration due to
  gravity on a particular planet.
• For instance g on earth is 9.8 m/s²
• The larger the planet, the _____ the
  gravitational force.