Transcript Force

Balanced and
Unbalanced Forces
FORCE
A PUSH OR PULL EXERTED ON AN OBJECT.
Balanced and Unbalanced forces
FORCE
Force
is measured using the SI
( International System of Units )
unit of newton (N).This is
named after Sir Issac Newton.
This unit is used to measure
the strength of a force.
BALANCED

If the two objects are the same size but in
opposite directions, they will balance out.
These forces are called balanced forces
`

In a game of tug of war when both the teams
pull the rope with equal and opposite forces,
then the rope remains stationary as the
forces acting on it are equal and opposite
and their resultant is zero.
BALANCED FORCES
500 N
500 N
`

If the block is pulled from both sides with the
same effort the block remains stationary.
The forces are equal and opposite and
therefore the block does not move. The
resultant of the forces acting on the body is
zero.
`

If you squeezed a rubber ball between the
palms of your hands. What would you observe?
The shape of the rubber ball changes. The
forces applied on the ball are equal and
opposite and the resultant of these forces does
not move the object, instead the object gets
deformed as long as the force is applied. This is
a temporary deformation.
BALANCED

Since these two forces are of equal
magnitude and in opposite directions, they
balance each other. The person is at
equilibrium. There is no unbalanced force
acting upon the person and thus the person
maintains its state of motion.
UNBALANCED FORCES

Forces that produce a nonzero net force ( the
overall force on an object when all the
individual forces acting on it are added
together), which changes an object’s motion.
UNBALANCED FORCES
400 N
200 N
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
The figures show a block of wood on a table.
When the block is pulled at point A, it begins
to move towards the left and if the block is
pulled at the point B it moves towards the
right.
UNBALANCED AND BALANCED
DEMONSTRATION

Balanced and Unbalanced Demonstration
BALANCED AND UNBALANCED FORCES
Push and ____ are forces.
 The force of gravity pulling towards the Earth is
called _______
 An object placed in water has a force called
_______ pushing up on it.
 When the forces acting on an object are equal and
opposite, they are called _______
 If the forces are balanced, the object will stay still
or carry on at the same speed in the same
direction.

IF TWO DIFFERENT FORCES ARE ACTING ON
AN OBJECT IN OPPOSITE DIRECTIONS, THE
OBJECT WILL;
A. stay in the same place
 B. move in the direction of the larger force
 C. move in the direction of the weaker force

CHOOSE ALL THAT APPLY… IF THE FORCES
ARE BALANCED AN OBJECT WILL:
A. stay still
 B. slow down
 C. carry on at same speed in the same
direction

TAKE A QUICK LOOK
Name at least three
types of natural
forces!
NEWTON'S SECOND LAW OF MOTION

The relationship between an object's mass m,
its acceleration a, and the applied force F is F =
ma. Acceleration and force are vectors (as
indicated by their symbols being displayed in
slant bold font); in this law the direction of the
force vector is the same as the direction of the
acceleration vector.
F = ma
 The equation form of Newton's second law allows
us to specify a unit of measurement for force.
Because the standard unit of mass is the kilogram
(kg) and the standard unit of acceleration is
meters per second squared (m/s2), the unit for
force must be a product of the two -- (kg)(m/s2).
This is a little awkward, so scientists decided to
use a Newton as the official unit of force. One
Newton, or N, is equivalent to 1 kilogram-meter per
second squared. There are 4.448 N in 1 pound.


If you want to calculate the acceleration, first
you need to modify the force equation to get
a = F/m. When you plug in the numbers for
force (100 N) and mass (50 kg), you find
that the acceleration is 2 m/s2.
NOW LET'S SAY THAT THE MASS OF THE SLED STAYS AT 50 KG AND THAT
ANOTHER DOG IS ADDED TO THE TEAM. IF WE ASSUME THE SECOND DOG PULLS
WITH THE SAME FORCE AS THE FIRST (100 N), THE TOTAL FORCE WOULD BE 200
N AND THE ACCELERATION WOULD BE 4 M/S2.
NOTICE THAT DOUBLING THE FORCE BY ADDING ANOTHER DOG DOUBLES THE
ACCELERATION. OPPOSITELY, DOUBLING THE MASS TO 100 KG WOULD HALVE
THE ACCELERATION TO 2 M/S2.
FINALLY, LET'S IMAGINE THAT A SECOND DOG TEAM IS ATTACHED TO THE
SLED SO THAT IT CAN PULL IN THE OPPOSITE DIRECTION.


If two dogs are on each side, then the total force
pulling to the left (200 N) balances the total force
pulling to the right (200 N). That means the net force
on the sled is zero, so the sled doesn’t move.


This is important because Newton's second law is
concerned with net forces. We could rewrite the law to
say: When a net force acts on an object, the object
accelerates in the direction of the net force. Now
imagine that one of the dogs on the left breaks free and
runs away. Suddenly, the force pulling to the right is
larger than the force pulling to the left, so the sled
accelerates to the right.
What's not so obvious in our examples is that the sled is
also applying a force on the dogs. In other words, all
forces act in pairs. This is Newton's third law -- and the
topic of the next section.
NEWTON’S LAW OF MOTION

http://www.youtube.com/watch?v=UVdqxYyFR
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NEWTON'S THIRD LAW OF MOTION

For every action there is an equal and opposite
reaction.
NEWTON'S FIRST LAW OF MOTION

Every object in a state of uniform motion tends
to remain in that state of motion unless an
external force is applied to it.
BALANCED FORCE
250 N
250 N

If two forces are acting on an object in opposite
directions, the object will move in the direction
of the larger force