Download Newton*s Laws - MTHS - Kelly

Enduring Understanding: Studying
dynamics (causes of motion) has had a
profound effect on the way humans view their
world.
Essential Question: What may be
accomplished by understanding dynamics?
Essential Question: How may we
symbolically represent dynamics information?
Essential Question: How are dynamics a
predictor of kinematics?
2 Issac Newton’s
What do you think?
Newton’s Laws
-Built on Galileo’s ideas
-If I have seen farther it is
by standing on the
shoulders of Giants
Today, we agree with
Newton’s Laws of Motion.
These laws of
motion differ
from the views
of Aristotle and
the Ancient
Greeks.
Aristotle on Motion
-Natural Motion : Vertical
Motion. Falling objects or
smoke rising.
No force
recognized.
Violent Motion
Was motion with a
visible force.
A push or a pull.
It was also believed that an objects
natural position was at rest.
Newton’s First Law
Law of Inertia
Every object continues in a state of
rest, or of motion in a straight line
at constant speed, unless it is
compelled to change that state by
forces exerted upon it.
Inertia: resistance to change
A New View of Motion
All motion is now seen as
caused by Forces.
Friction is identified as a cause of
slowing and speeding.
Falling objects are linked with gravity.
Mass – Amount of Inertia
More mass means more resistance to
change.
Mass is measured in kilograms (kg).
Mass is not weight.
1 kg of mass weighs 9.8 Newtons(N)
Weight is a downward force due to
gravity.
->The unit for weight is the
Newton. The Newton is a
derived unit.
->To calculate weight, mass and
gravity are involved.
-> w = m x g
->w is weight, m is mass in (kg)
g the acceleration due to gravity is
9.8 (m/s2) at sea level on earth.
Calculations Involving Weight
Unless told otherwise, assume the problems take
place at sea level on earth.
What is the weight of a 1 kg object?
w = mg
w = 1(kg) x 9.8(m/s2 ) = 9.8(N)
The Newton (N) is derived from the
units (kg), (m)eter and (s)econd.
What is the weight of a 2 kg object?
19.6 N
What is the weight of a 15 kg object?
147 N
What is the mass of a 100 N object?
10.2 kg
What is the mass of a 250 N object?
25.5 kg
Weight, the force due to gravity
always acts on an object.
The Normal Force is also known
as the support force.
the weight and
the normal
force are equal
in size and
opposite in
direction.
Net Force
At least one force is acting
on every object at all
times.
Net Force is the total of all
the forces.
All Forces are measured in Newtons.
In the tug of war, if the team on the
left pulls with a force of 1200 N and
the team on the right pulls with
1000 N, what is the net force?
Answer
200 N to the left
Forces Can Be Added As
Vectors.
A free body
diagram is used
to identify the
forces acting on
an object.
More Free Body Diagrams
Equilibrium
At Equilibrium all forces are
balanced. The net force is zero.
A number of
large forces
act on a
bridge. What
are they?
What happens if the
forces acting on a bridge
are not in equilibrium?
Can an object be at
equilibrium and still be
moving?
Yes
According to The Law of
Inertia, an object in
motion will stay in motion
at the same speed if all of
the forces are in balance.
If the forces become out
of balance, the object will
slow down, speed up or
change direction.
Free Body Diagram Practice
A box is at rest on a table. Draw a
free body diagram of the forces
acting on it.
_____________________________________________________________
normal force
_____________________________________________________________
weight
The normal force and the
weight always act on an
object on a surface.
A person pushes a box to the
right. Draw a free body
diagram of the forces acting on
it.
_________________________________________________________
normal force
applied force
friction
____________________________________________________________
weight