What is Force?

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What is Force?

• A force is a push or pull that causes an object
  to move faster or slower, stop, change direction,
  or change size or shape.
• Without force, nothing would ever move.

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(No Transcript)
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Lets review information about forces!
http//www.engineeringinteract.org/resources/parkw
orldplot/flash/concepts/allaboutforces.htm
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Magnetic Force
Magnetism is the force of pushing or pulling
between magnetic poles. It acts at a distance
and cannot be seen. Materials that create this
force are said to be magnetic and are called
magnets.
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When like poles of magnets are near each other, a
repulsive force exists, and the magnets move away
from each other if the force is great enough.
When opposite poles of magnets are near each
other, an attractive force exists and the magnets
move toward each other if the force is great
enough. The closer the objects, the greater the
magnetic force. The magnetic force is greatest
at the poles of magnets.
http//www.engineeringinteract.org/resources/parkw
orldplot/flash/concepts/magneticforces.htm
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Lets look at what we already know about forces.
What would happen with these pairs of magnets?
Will they attract or repel each other? Write and
draw what you think will happen, and
then we will see if you are correct.
1.
2.
3.
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Gravitational Force

• Gravity is a force that pulls all objects toward
  each other.

http//www.engineeringinteract.org/resources/parkw
orldplot/flash/concepts/gravity.htm
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• The force of gravity causes two objects of
  different weights to fall to the ground at the
  same time.
• The force of gravity is a pull that attracts
  objects to each other. This attraction is not
  noticeable unless one of the objects is very
  large (like a planet, moon, or the Sun). The
  force of gravity between Earth and anything on it
  is extremely noticeable because the mass of Earth
  is so large.
• The pull of Earths gravity makes any object fall
  to the ground. As The Moon goes around Earth,
  its gravity pulls on Earth causing water in the
  oceans to move toward the Moon.

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• Earths gravity also pulls on the Moon. This
  force of gravity keeps the Moon moving around
  Earth. Similarly, the pull of the Suns gravity
  keeps Earth moving around the Sun.

http//www.seed.slb.com/en/scictr/watch/skydiving/
galileo_pisa.htm
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Which will hit the ground first?
They travel at the same speed! The size of the
mass does not change the rate of speed that
objects fall.
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Which will hit the ground first?
The paper was slowed by air getting trapped under
as it fell. Shape of object may affect the speed
in which it falls!
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Frictional Forces

• Friction is the force that is applied by a
  surface as an object moves across it.
• It is always present when two surfaces rub
  together.
• Friction is affected by the nature of the surface
  (bumpy, smooth) and upon the degree to which they
  are pressed together .

http//www.engineeringinteract.org/resources/parkw
orldplot/flash/concepts/friction.htm
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Friction

• Some forces can be seen when a moving object is
  touching another object, for example, a toy
  sliding across a table and slowing down.
• Friction is the force that opposes motion between
  two surfaces that are touching.
• The rougher the surfaces are, and the harder they
  press together, the more friction there will be.

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Friction

• Friction can be reduced by using lubricants (like
  motor oil, wax, or grease), by making surfaces
  smoother, or by using rollers.
• Friction occurs in liquids and gases as well as
  between solids.
• Without friction, it would be very hard to slow
  or stop the motion of objects.

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high
high
low
low
low
low
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• The effect of friction can be changed in the
  following ways

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Surface
Texture
of the

• The rougher the surface, the greater the
  friction.
• Smooth surfaces reduce friction.
• So, carpets have more friction that tile floors.
• Soles of shoes have rough textures to increase
  friction between the shoes and the floor so that
  it is possible to walk without slipping

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Amount of Surface Area

• The greater the surface area, the greater the
  friction.
• If more surface of an object touches another
  object, the friction will be greater. If tires
  of a car or truck are larger, more surface area
  of the tire will touch the road making friction
  greater. Trucks have larger tires to make it
  easier for them to stop or slow down.

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Lubrication

• Lubricants- a substance put on a surface to
  reduce friction

Without lubrication, moving parts of machines
would slow down or stop very quickly.
We use oil in a car to reduce friction on the
motor.
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Motion

• The motion of an object can be described by its
  position, direction of movement, and speed.

How do we know this flag is in motion?
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Speed

• One way to describe motion is speed.
• Speed is a measure of the distance an
• object moves in a certain amount of time.
• Speed is a measure of how fast an object is
  moving.
• Motion is the change in position of an object
  over time when compared with a reference point.

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Position

• The position of an object is its location
  relative to another object (the reference point).
  
• For example, we can use the words above,
  below, beside, behind, ahead of plus the
  distance from the other object.
• The distance (length) from the reference point
  changes when the object moves.

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Point of Reference

• Point of reference-your point of motion when you
  observe a motion

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Starting Position

• Speed, ramp height, length, and surface type can
  affect motion.
• The higher the position, the greater the speed
  and distance will be in the objects motion.

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Balanced and Unbalanced Forces

• http//www.engineeringinteract.org/resources/parkw
  orldplot/flash/concepts/balancedandun.htm

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Balanced Forces

• Balanced forces are forces equal in size and
  opposite in direction.
• Neither object moves because it is equal in both
  directions.

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Unbalanced Force

• Unbalanced forces occur when one force is greater
  than its opposite force. They cause the objects
  motion to speed up, slow down, or stop. The
  object moves in the direction applied by the
  greater force.
• Unbalanced forces cause a non-moving object to
  start moving. They affect the rate and direction
  of motion in objects.

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Unbalanced Force
Think of the game tug-of-war If you are the only
one pulling on your side, and on the other side
there are three people pulling, the forces are
unbalanced because it is three pulling against
one. However, if three people were on each
side, the forces would be more balanced, making
the rope move less quickly.
The Jeep pulling the car is another example of an
unbalanced force because the Jeep has a bigger
and more powerful force. If the Jeep was
pulling another Jeep, the forces would be
balanced and neither would move very far because
the force being used is the same amount.
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Rate of motion

• Rate of motion is the speed of the object or how
  fast or slow the object is moving.
• Unbalanced forces can cause the speed or the rate
  of motion to change by increasing, decreasing, or
  stopping the motion.

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Direction

• If the total force is unbalanced the forces
  acting on an object are not equal in all
  directions.
• Thus, the unbalanced force causes a change in the
  direction of the motion as follows
• The object moves away from the unbalanced force
  if it is a push, or toward the unbalanced force
  if it is a pull. The object will move in the
  direction of the greatest force acting on it.

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• Speed of an object is the measure of the distance
  (change in position) an object moves in a given
  amount of time.
• Speed is distance divided by time, so you can
  take the value on the Y axis and divide it by the
  value on the X axis.

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Slower Speed The line on the graph is a flatter
line, illustrating a slower speed
Faster Speed The line on the graph is a steeper
line, illustrating a faster speed
Speed Stopped The line illustrates a constant
speed from 0-5 seconds. From 5 to 10 sec, the
line is flat with no increase in position. This
graph illustrates an object that is stopped
between 5 and 10 seconds.
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• A change in force or mass affects the motion of
  an object as follows

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Force

• As the force increases, the speed of an object
  increases.
• As the force applied to an object is decreased,
  the object will move slower than the object that
  was given a greater push or pull.
• If there is no friction (for example, in outer
  space), an object that is already moving does not
  need a force to keep it moving.
• Because of friction, however, an object slows or
  stops eventually.

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Mass

• As the mass increases, the speed of an object
  decreases if the force remains the same.
• The speed decreases as the objects mass
  increases.
• It is much harder to change the speed of a heavy
  object than a light object.
• An object with a small mass is easier to stop or
  cause a change in motion than an object with a
  large mass.

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All About Forces

• http//www.engineeringinteract.org/resources/parkw
  orldplot/flash/concepts/allaboutforces.htm