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Chapter 13
Forces of Motion
Velocity n.
• The speed and direction of an objects motion.
• The velocity of the train was 30 meters per
second north.
• The velocity of the
was 50 meters
per second south.
Lesson 1 How can you describe
motion?
• Motion
is all around you.
• Different kinds of motion happen at different
rates.
• There are many different types of motion –
. constant
, variable, periodic, vibrational ,
and circular.
http://studyjams.sch
olastic.com/studyjam
s/jams/science/force
s-and-motion/forceand-motion.htm
Speed and Velocity
• Speed is how far an object moves during a certain
amount of time
. Distance/time
• Ex 100m/20s = 5m/s
• Motion is always measured in relationship to
some location called a point
of reference.
• Speed and velocity are not the same
.
• Velocity describes the speed
and the
direction of an object’s motion. Ex. North, south,
up, or down.
Review
1) What two things do you need to know to find
an object’s velocity?
2) Robert moved 28 m in 4 sec. Tallana moved
600 m in 2 min. List these people and their
speeds in order from fastest to slowest.
3) Motion is always measured in relationship to
some location called a
of reference.
4) What is the formula for speed?
Force
.
• A push or pull that acts on an object.
• The force of the wind was very strong.
• Write you own sentence using this starter.
The force of
.
• Is gravity a force?
Work
.
• Done when a force moves an object.
• Work is done only when the object moves at least
partly in the same direction in which the force is
applied.
• Work = force x distance
• Is work done if I am pushing on the wall?
• Is work being done if I am pushing a chair across
the room?
• If I am holding on to a ball is work being done?
Power
.
• Rate at which work is done.
• Since running up the hill is faster than walking,
the amount of power needed to run is greater.
• Power = work/time
• If I do work faster is there more power
involved?
Lesson 2 What are Forces?
• A force is a push or pull
that acts on an
object.
• Forces can make a moving object speed up, slow
down, or change directions .
• Forces have both magnitude and direction.
Magnitude measured in Newtons (N)
Gravity
• Every object in the universe exerts a gravitational
pull on every other object. Only large objects
such as Earth’s
are strong enough to be felt.
• An object’s weight is the amount of
gravitational force between it and Earth. This
force depends on Earth’s size, mass, and how
far above Earth the object is.
• Your weight
would be less if you are flying
or on another planet, because of less gravity .
Magnetism and Electricity
•
•
•
•
Magnetism – force that pushes
and pulls.
A magnets force is greatest at a magnet’s poles .
Every magnet has a south and north pole.
attract . If you have
North and south poles
a north and north pole they will repel.
• Objects get electrically charged when they gain or
lose electrons.
• Electrons often move from one object to another
when the objects are rubbed together.
• Gravity, magnetic, and electric forces increase as
objects get closer together.
• Magnetism and electricity can be blocked by
certain objects.
Gravity
•
can’t be blocked.
• Electricity and magnetism can push or pull.
• Gravity only can pull
.
http://studyjams.scholastic.com/studyjams/ja
ms/science/forces-and-motion/fgravity-andinertia.htm
Friction
• Friction is the force
that results when
two materials rub against each other.
• Friction slows down objects or keeps them
from
to move.
starting
• Speed, shape, or texture affect the amount
of friction with other objects.
• Share an example of friction.
• Air and water resist motion when a moving
objects tries to go through them.
Work and Power
• Work is done when a force .moves an object.
• Work is measured in Joules
• If the force applied to an object does not move
the object, then no work has been done.
• Holding an object requires a force, but since the
object does not move, no work is done.
• Power
is the rate at which work is done.
When work is done faster power is increased .
Review
1) Define force.
2) As objects get closer together gravity,
electricity, and magnetism do what?
3) How does friction affect the movement of an
object?
4) When is work done?
5) What is power?
Inertia
.
• The tendency of an object to resist any change in
motion. Unless a force acts on an object, the
object will remain in constant motion.
• Objects with more mass have more inertia than
objects with less mass.
• Ex. When a car turns directions your body tends
to keep moving in the direction it was moving.
• Inertia - roller coaster.
• The seat belt prevents the test dummy’s inertia
from carrying the dummy through the
windshield. Think of some other examples.
Lesson 3 What are Newton’s laws of
motion?
• Newton’s laws of motion explain why objects
like a ball move the way they do.
• Different forces can act on an object at the time.
They may act in different directions .
• All the forces acting on an object equal the net
force.
• The net force will determine whether the object
starts moving, stops
, or changes direction.
• Isaac Newton – Newton’s laws, law of gravitation,
and used math in studying nature.
Newton’s 1st Law
• Says that unless a net force acts on an object the object
will remain in constant motion. An object at rest
stays at rest until a net force acts on it.
• The tendency of an object to resist any change in
motion is inertia.
• Objects with a lot of mass have more inertia than
those that don’t have much mass.
• Example When you turn directions in a car or riding a
roller coaster.
http://www.youtube.com/watch?v=ZFoG7HRF2mE
http://studyjams.scholastic.com/studyjams/ja
ms/science/forces-and-motion/inertia.htm
Newton’s 2nd Law
• Describes how acceleration, mass, and net
force are related.
• Acceleration is the rate at which the velocity of
an object changes over time.
• Acceleration = force/mass
• The stronger the force acting on an object, the
more that object will accelerate
.
• http://www.youtube.com/watch?v=iwP4heW
Dhvw http://studyjams.scholastic.com/studyjams/ja
ms/science/forces-andmotion/acceleration.htm
Newton’s 3rd Law
• When one object exerts a force on a second
object, the second object exerts a force on the
first object.
• Action- reaction law of motion. Forces are
always equal and opposite and always occur
in pairs.
• This happens all around us. It is impossible to
have one force without an equal and opposite
force!
• Ex bumper cars
• http://www.youtube.com/watch?v=cxVBbgFJo6Y
http://studyjams.scholastic.com/studyjams/jams/sc
ience/forces-and-motion/action-and-reaction.htm
Review
1)
2)
3)
4)
What is Newton’s first law of motion?
Describe Newton’s 2nd law of motion.
Explain Newton’s 3rd law of motion.
Which of Newton’s laws of motion is
demonstrated by a hammer pounding a nail
into a board?
5) What are all the forces acting on an object
called?
Machine
.
• A device that changes the direction or the
amount of force needed to do work.
• Ex. Wheel and axle, pulley, or lever.
• They used a machine to help make their work
easier.
• Think of an example of when you would want
to use a machine to do work.
Lesson 4 What are simple machines?
• Remember work is done when a force causes an
object to move .
• A machine changes the direction or amount of
force needed to do work.
• Simple machines are machines with few parts.
• Ex. Wheel and axle, pulley, inclined plane, and
lever.
• Machines don’t reduce the amount of work that
needs to be done they just make it easier .
http://studyjams.scholastic.com/studyjams/ja
ms/science/forces-and-motion/simplemachines.htm
Pulley
• Consists of a rope or cable that runs through a
grooved wheel.
• Flagpoles
and drapery rods use pulleys.
• A block and tackle is a system of pulleys that
make it easier to lift very heavy objects.
Wheel and Axle
• Made up of a circular object such as a
doorknob, and a shaft.
• They reduce the amount of force needed
to do work.
• Steering wheel of a car and pulling a bucket
out of a well with a crank are some examples.
Lever
• Where a bar rotates around a fixed point called a
. fulcrum .
• Levers do work using the bar, fulcrum, a load, and
a force
you apply.
• As the position of the fulcrum changes the
amount of force needed to move the box will
change.
• The farther the fulcrum is from the person using
the lever, the easier
the lever is to use.
• Ex. Wheel barrow, pliers, clothespins.
Inclined planes
• A ramp
is an example of an inclined
plane.
• It consists of a flat surface with one end higher
than the other.
• Can be big or small.
• Other inclined planes include screws (inclined
plane is wrapped around it) and doorstops.
Complex Machines
• A machine that uses two
or more
simple machines.
• Many complex machines use electricity ,
gravity, burning fuel, human force, or
magnetism.
• Example Go carts, sailing ships.
• What would be some other examples of
complex machines?
Review
1) What are two examples of a wheel and axle
that can make work easier?
2) What are all of the parts of a lever?
3) What is a complex machine?
4) What simple machine are you using when
you raise or lower a flag on a flagpole?