Physics: work, force and energy

PHYSICS: FORCE, ENERGY AND WORK
TEACHER: Vergie M. Bateriza

LESSON OBJECTIVE
Study the concept of force, energy and work and its
relationship;
Understand how to compute the value of net force
value of Mathematically work done situation in a
given; and
Identify the different conditions for us to say that
work is done.

FORCE
In Physics: force is the push or pull
applied on an object.

FORCE
Force can also change the speed and
direction of a moving object.

FORCE
If enough force is applied, it can also change the
shape or size of an object

Categories of forces:
1. Contact forces are those types of forces that result when the two
interacting objects are perceived to be physically contacting each
other.

2. action-at-a distance force
Gravitational force, electrical force, magnetic force

BALANCED FORCE
forces that are equal in magnitude and in opposite
direction so there will be no motion in an object
Let us study this illustration:
1. It was observed that a 50 kg object is
being pushed to opposite directions,
we have observed that a 70 Newton of
force is being applied to push the said
object to the right and on the other
side, the same amount of force is being
exerted pushing to the left direction.

BALANCED FORCE
2. The two elephant were pulling
a log in an opposite direction
using a 200 Newton force.

BALANCED FORCE
3. Suppose two boys are pushing the 190 kg
heavy crate with 25 newtons of force to the
right and another guy is pushing the said crate
to the left with 50 newtons of force to the left,
what will be the net force that will act on the
object? Will the object move?

NET FORCE
 is the vector sum of forces acting on a particular or body.
ADD the values of the forces going to the same direction to get
the NET FORCE
SUBTRACT the values of the forces going to the opposite direction
to get the NET FORCE

UNBALANCED FORCE
 a force where two forces acting in opposing directions on a
body, are not equal in magnitude and in size.
 When force is applied on an object, resulting in the
movement of that object work is said to be done.
1. On this illustration it shows that there
were three persons pulling the rope to
the opposite sides. It is notable that
the other group exerted 400 Newton
force while the other groups exerts 300
Newton force.

UNBALANCED FORCE
LEFT RIGHT NETFORCE
400 N 300 N = 100 N To
the left

UNBALANCED FORCE
1. Joy is pushing the piano going to the
right by exerting 35 Newtons force
while Joey is pulling the piano to the
right by exerting 30 Newton force

UNBALANCED FORCE
JOY JOEY NETFORCE
35 N 30 N = 65N to
the right

Difference between BALANCED and
UNBALANCED FORCE
condition balanced Unbalanced
Net force zero Greater than zero
Magnitude
(forces)
equal Not equal
direction opposite Same or opposite
Objects position At rest Moves in the
direction with
greater force.

Assessment:
 With your groupmates examine if the illustrations below shows balanced force by
yelling “mine” and if it shows unbalanced force yell “yours”.
1.___________

Assessment:
 Tell if the illustrations below shows balanced force by yelling “mine” and if it shows
unbalanced force yell “yours”.
2.___________

Assessment:
3.___________

Assessment:
4.___________

Assessment:
5.___________

Assessment:
 With your groupmates examine if the illustrations below shows balanced force by yelling “mine”
and if it shows unbalanced force yell “yours”.
 Lets check!!!
1. Mine
2. Yours
3. Yours
4. Yours
5. Mine

Energy In Physics, energy is the
capacity to do work

Kinetic energy exists whenever an object which has mass is in
motion with some velocity. Everything you see moving about
has kinetic energy. The kinetic energy of an object in this case
is given by the relation:
KE = (1/2)mv2
m=mass of the object
V=velocity of the object
The greater the mass or velocity of a moving object, the more
kinetic energy it has.

The greater the mass or velocity of a moving object, the more
kinetic energy it has.

Potential energy exists whenever an object which has mass has a
position within a force field. The most everyday example of this is
the position of objects in the earth's gravitational field. The
potential energy of an object in this case is given by the relation:
PE = mgh
PE = Energy (in Joules)
m = mass (in kilograms)
g = gravitational acceleration of the earth (9.8 m/sec2)
h = height above earth's surface (in meters)

Law of Conservation of Energy-
Energy can neither be created nor
destroyed. Energy is always changing
from one kind to another. The total
energy of an object never changes.

Work
Work is the product of the
force exerted on the object
and the displacement of the
object along the direction of
the force. (parallel
relationship)

Work is done
 For us to say that work is being done,
there are three conditions that must be
met:
1. There must be a presence of force
2. The object has to move a certain
distance called displacement
3. The movement of the object must
be in the same direction of the
applied force.

Activity
 Let us analyze if the following illustrations shows the concept of work:
1. A man pushing the wall- is there a work done?
Conditions Present/absent
Presence of force
Presence of
displacement
Parallel relationship
of force and
displacement

Activity
Presence of force present
Presence of
displacement
Absent
of force and
displacement
Absent

Activity
2. A man pulling a box-is there a work done?
Presence of force
Presence of
displacement
of force and
displacement

Activity
Presence of
displacement
present
of force and
displacement
present

Activity
3. A man walking while reading a book -is there a work done?
Presence of force
Presence of
displacement
of force and
displacement

Activity
Presence of
displacement
present
of force and
displacement
absent

Let us compute mathematically the value of
work in a situation

Physics: work, force and energy

What is the underlying relationship
between force-energy-and-work?
When force is applied and the object move in
parallel direction with the applied force work is
done.
In order for anyone or anything to do work it must
have energy.
In doing work, energy is transferred. When the
object does the work it losses energy and when the
object is done on the object it gains energy.

Assessment:
 Tell if the illustrations below shows work is done by writing “mine” and if it shows
work is not done write “yours” on your answer sheet
1
2
3
4

Assignment:
At home, list down at least 5 real life scenarios. Ask
your family members to portray the scenario, take a
picture and print it in a long bond paper. Label each
picture by using an arrow that represent the force
applied, and the displacement of the object.

Physics: work, force and energy

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