Transcript Grade 10 Force PowerPoint II

Force - a push or pull on an object
“The Force is what gives a Jedi his power. It’s an
energy field created by all living things. It surrounds
us, penetrates us, and binds the galaxy together”
-Obi-Wan Kenobi-
Force is a vector quantity, therefore it has
direction and magnitude.
A free-body diagram is a model which represents all
the forces acting on a system.
Net Force = vector sum of all the forces acting
on an object.
You and your friend are pushing a stalled car. Your friend applies 230N
of force while you apply 330N of force in the same direction.
• What is the net force on the car?
• If you push in opposite directions what is the net force on the car?
Newton’s Second Law of Motion
The rate of acceleration of an object is directly
related to the mass of the object and the net
force applied to the object.
• a = Fnet / m or
Fnet = ma
• 1 Newton = the
force required to
accelerate 1 kg
by 1 m/s2
(N = kg•m/s2)
Remember, a is directly related to the Fnet applied to
the object and the m of the object.
How much force is applied in both of these
examples?
• What observations can we make?
Using Fnet = ma to explain freefall
• Since the
force acting
upon the
more massive
object is
greater the a
is always
equal!
Newton’s First Law of Motion
An object at rest will remain at rest and an object
that is moving will continue to move in a straight
line with constant speed, if and only if the net
force acting upon that object is zero.
Name all the forces acting upon these systems.
Which systems have zero net force?
Remember when Fnet = 0 then a = 0, but it can still have v.
• A book sitting on a table.
• A ball thrown horizontally on earth.
• A car driving at a constant velocity on the
highway.
• A ball thrown horizontally in space.
• A ball rolling on the ground.
• An elevator ascending up the 12th floor.
An object is at equilibrium if its net force is equal to zero.
Inertia - the tendency for an object to resist change.
http://ircamera.as.arizona.edu/NatSci102/NatSci102/movies/law1_an.gif
• Why do you fall backward on the subway when
the train takes off?
• Why do you fall forward on the subway when the
train stops?