Download force

What is a Force?
FORCE = Any push or pull which causes
something to move or change its
speed or direction
What is a Force?
Forces can be BALANCED or UNBALANCED


Balanced forces are equal in size and
opposite in direction
UnBalanced forces are not equal in size
and/or opposite in direction. If the
forces on an object are UNBALANCED,
we say a NET force results.
What is a Force?
Can you think of examples of forces?

Balanced Forces?

Unbalanced Forces?
Force
I.
Force
A. a push or pull that one body exerts on
another
B. What forces are being
exerted on the football?
Fkick
Fgrav
Measuring Forces
I.
I.
Forces are
measured in
newtons
(kg . m/s2).
Forces are
measured using a
spring scale.
Force
I.
Balanced Forces
A. forces acting
on an object
that are
opposite in
direction and
equal in size
B. no change in
velocity
Force
I.
Net Force
A. unbalanced forces that are not
opposite and equal
B. velocity changes (object
accelerates)
Fnet
Ffriction
Fpull
N
N
W
ConcepTest 2
You are a passenger in a car and not
wearing your seat belt.
Without increasing or decreasing its speed,
the car makes a sharp left turn, and you
find yourself colliding with the right-hand
door.
Which is the correct analysis of the
situation? ...
ConcepTest 2
1. Before and after the collision, there is
a rightward force pushing you into the
door.
2. Starting at the time of collision, the
door exerts
exerts aa leftward
leftward force
force on
on you.
you.
door
3. both of the above
4. neither of the above
ConcepTest 1
TRUE or FALSE?
The object shown in the diagram must be at
rest since there is no net force acting on it.
FALSE! A net force
does not cause motion.
A net force causes a
change in motion, or
acceleration.
Taken from “The Physics Classroom” © Tom Henderson, 1996-2001.
What is Gravity?
GRAVITY: An attraction force between
all masses
 Newton’s universal law of
gravitation: Every object in the
universe exerts a gravitational
attraction to all other objects in the
universe
 The amount of gravitational force
depends upon the mass of the objects
and the distance between the objects
What is Gravity?



The greater the mass, the greater
the force
The greater the distance, the less
the force
Acceleration due to gravity = 9.8
m/s/s or 9.8 m/s2
Gravity
A.force of attraction between
any two objects in the universe
B.increases as...
1.mass increases
2.distance decreases
Gravity
I.Who experiences more gravity - the
astronaut or the politician?
I.Which exerts more gravity the Earth or the moon?
less
distance
more
mass
Gravity
I.Would you weigh more on Earth or
Jupiter?
A.Jupiter because...
greater mass
greater gravity
greater weight
What is Motion?
Motion: A change in position of an
object compared to a reference
point
What is Friction?
Friction = A force that opposes or slows
down motion
 Caused by the physical contact
between moving surfaces
 The amount of friction depends upon
the kinds of surfaces and the force
pressing the surfaces together
 Changes motion into heat
Friction
A. force that opposes motion
between 2 surfaces
B. depends on the:
1. types of surfaces
2. force between the surfaces
I.
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)