2. Force
Two types of forces
Contact force
Force caused by physical contact
Field force
Force caused by gravitational attraction
between two objects
3. Isaac Newton
Born 1642
Went to University of Cambridge in England as
a student and taught there as a professor after
Never married
Gave his attention mostly to physics and
mathematics, but he also gave his attention to
religion and alchemy
Newton was the first to solve three mysteries
that intrigued the scientists
Laws of Motion
Laws of Planetary Orbits
Calculus
4. Three Laws of Motion
Newton’s Laws of Motion are laws
discovered by Physicist and
mathematician, Isaac Newton, that
explains the objects’ motions depending
on forces acted on them
Newton’s First Law: Law of Inertia
Newton’s Second Law: Law of Resultant
Force
Newton’s Third Law: Law of Reciprocal
Action
5. Newton’s First Law
An Object at rest remains at rest, and an
object in motion continues in motion with
constant velocity (that is, constant speed
in a straight line), unless it experiences a
net external force.
The tendency to resist change in motion
is called inertia
People believed that all moving objects
would eventually stop before Newton came
up with his laws
6. Friction
A force that causes resistance to motion
Arises from contact between two
surfaces
If the force applied is smaller than the
friction, then the object will not move
If the object is not moving, then ffriction=Fapplied
The object eventually slips when the
applied force is big enough
7. Friction
Friction was discovered by
Galileo Galilee when he
rolled a ball down a slope
and observed that the ball
rolls up the opposite slope to
about the same height, and
concluded that the
difference between the initial
height and the final height is
caused by friction.
Galileo also noticed that the
ball would roll almost forever
on a flat surface so that the
ball can elevate to the same
height as where it started.
8. Two types of Friction
Static Friction
Friction that exists
while the object is
stationary
If the applied force on
an object becomes
greater than the
maximum of static
friction, then the object
starts moving
fstatic≤μstaticn
Kinetic Friction
The friction that exists
when an object is in
motion
F-fkinetic produces
acceleration to the
direction the object is
moving
If F=fkinetic, then the object
moves at constant speed
with no acceleration
fkinetic= μkineticn
Kinetic friction and the
coefficient of kinetic
friction are smaller than
static friction and the
static coefficient
9.
10. Newton’s First Law
When there is no force
exerted on an object, the
motion of the object remains
the same like described in
the diagram
Because the equation of
Force is F=ma, the
acceleration is 0m/s². So
the equation is
0N=m*0m/s²
Therefore, force is not
needed to keep the object
in motion, when
The object is in
equilibrium when it does
not change its state of
motion
11. The car is traveling rightward
and crashes into a brick wall.
The brick wall acts as an
unbalanced force and stops
the car.
12. The truck stops when it
crashes into the red car.
But the ladder falls in front
of the truck because the
ladder was in motion with
the truck but there is
nothing stopping the
ladder when the truck
stops.
13. Newton’s Second Law
The acceleration of an object is directly
proportional to the net force acting on it
and inversely proportional to its mass
Fnet
Acceleration
14. Unbalanced Force and
Acceleration
Force is equal to
acceleration multiplied by
mass
When an unbalanced
force acts on an object,
there is always an
acceleration
Acceleration differs
depending on the
net force
The acceleration is
inversely related to
the mass of the
object
15. Net Force
Force is a vector
Because it is a vector, the net force can be
determined by subtracting the force that
resists motion from the force applied to the
object.
If the force is applied at an angle, then
trigonometry is used to find the force
Fnet
17. Gravitational Force
The force that exerts all objects toward
the earth’s surface is called a
gravitational force.
The magnitude of the gravitational force is
called weight
The acceleration due to gravity is
different in each location, but 9.80m/s² is
most commonly used
Calculated with formula w=mg
18. Newton’s Third Law
If two objects interact, the force exerted
on object 1 by object 2 is equal in
magnitude but opposite in direction to
the force exerted on object 2 by object 1
Forces always come in pair when two
objects interact
The forces are equal, but opposite in
direction
Fg
Fn
19. As the man jumps off
the boat, he exerts
the force on the boat
and the boat exerts
the reaction force on
the man.
The man leaps forward
onto the pier, while the
boat moves away from
the pier.
Newton’s Third Law
20. Force exerted by the wheels
Force exerted by the road
Newton’s Third Law
