Transcript What are Forces? - Ms. Y`s 5th Grade Class

Forces and Motion
Unit F
Ch. 1
What are forces?
• A force is a push or a pull.
• It causes objects to accelerate which
means to speed up, slow down, stop, or
change direction
• A force is equal to the mass of a moving
object times its acceleration.
• For every force there is an equal and
opposite reaction force.
Newton’s Second Law of Motion
• Force = mass X acceleration
• The greater the force, the greater the
acceleration.
• The greater the mass of an object the less
the acceleration if the same force is
applied.
What is friction?
• Friction is a force which opposes motion.
• Friction is an important force in our lives.
We rely on friction in many ways. An
athlete usually wears shoes which provide
him or her with a greater friction between
the shoe and the surface. We rely on
friction as an important aspect of our
motion. In what other ways does friction
play a role in our everyday lives?
From Glencoe Physical Science
What causes friction?
• There are two factors which affect
friction between two surfaces:
– Kind of surfaces in contact (rough or
smooth)
– Amount of force pressing the
surfaces together.
The rougher the surface and the
stronger the force between the
surfaces, the greater the amount of
friction.
Magnetism
• Magnetism is the force of repulsion or
attraction between poles of a magnet
• Opposite poles attract
• Same poles repel
What is Gravity?
• Gravity is a force of attraction between two
objects.
• Law of Gravitation – any two masses exert an
attractive force on each other. The amount of
attraction depends upon two things: the mass of
the objects and the distance between the
objects.
Gravity causes weight
• The weight of an object is caused by the
force of attraction between the earth and
objects on the surface of the earth.
Gravitation force is equal to weight, therefore…
What is weight?
• When an astronaut moves away
from the earth they “lose” weight.
Weight is caused by the force of
attraction between the earth and
objects on its surface. The greater
the distance an object has from
the earth, the less the force of
attraction which would exist.
What is projectile motion?
Balanced Forces
• Forces always work in pairs
• Balanced forces are equal size and
opposite in direction
• They cancel each other out
Unbalanced Forces
• Occur when one force is greater than its
opposite force
• Motion CHANGES: speeds up, slows
down, stops, or changes direction
• This is called Acceleration
Net Force
• Adding or subtracting the individual forces
gives a value, called a Net Force, of the
combined forces
• ONLY for unbalanced forces
• Same direction: add
• Opposite direction: subtract
• Direction of the net force acts in the same
as the larger force
Work and Effort
• Work is the use of force to MOVE an
object through distance
• If effort is applied but nothing moves there
is no work being done
• Work is measured in Joules
• Work= force (N) x distance (m)
Power
• Power is the amount of work done for
each unit of time
• It is a measure of how quickly someone or
something does work
• Watt is the unit of power
• Power(W)= Work(J)/Time(sec)
Machines
• Simples machines make work easier
• Pulley, wheel and axle, screw, inclined
plane, lever, wedge
• Compound machines like a shovel or
faucet are made of 2 or more simple
machines