1. Mechanics

2. Mechanics
The branch of physics that deals with the
action of forces on bodies and with motion,
comprised of kinetics, statics, and
kinematics.

3. Vector and Scalar Quantities
In your study of physics, you will encounter scalar and
vector quantities.
Examples of Vector quantities
1. Displacement:
An airplane flies a distance of 100 km in a easterly
direction.
2. Velocity
A car moves 60 km/h, 350 east of north.
3. Force
A force of 15 newtons acts on a body in an
upward direction

4. Examples of Scalar quantities
1. Mass
A load has a mass of 5 kg
2. Time
The car has reached its destination after 1 hour
3. Distance
The train has traveled a distance of 80 km.

5. Some quantities are expressed as (a number and a unit
of measure) only. These quantities are called
SCALAR.
Quantities that are expressed by a magnitude and
direction are called VECTORS
VECTOR is represented by an arrow. The arrow has
three important parts:
1. Arrowhead – indicates the direction of the vector.
2. Length of the arrow – represents the magnitude of
the vector
3. Tail – represents the origin of the vector

6. The Direction Guide

7. Example 1:
The ship sails 25 km north.
N
d = 25 km
Vector diagram
Given: d= 25km north
Scale: 1 cm = 10 km

8. Example 2:
The ship sails 20 km south, then 15 km east.
d1 = 20km
Given: d1 = 20km south
d2 = 15km east
Scale: 1 cm = 10 km
N
d2 = 15km
W E
d1 = 20km
d2 = 15km
S

9. Resultant Vector
Scalar quantities can be added and subtracted like
ordinary numbers provided the scalars have the same
unit.
For vectors, the sum depends on the direction of the
vectors.
The sum of two or more vectors is represented by a
single vector called RESULTANT.
This vector may be found by using the Graphical
method, the Pythagorean theorem, or the component
method.

10. Graphical Method
Carlito was observing an ant that crawled along a
tabletop. With a piece of chalk, he followed its path.
He determined the ant’s displacements using a ruler
and protractor. The displacement were as follows:
2cm east; 3.5cm,320 north of east; and 2.3 cm, 220 west
of north.
Given:
d1 = 2 cm east
d2 = 3.5 cm, 320 north of east
d3 = 2.3 cm, 220 west of north
dR = ?

11. Given:
d1 = 2 cm east
Solution: d2 = 3.5 cm, 320 north of east
d3 = 2.3 cm, 220 west of north
dR = ?
N
220 ___0
d3 = 2.3 cm
dr = 320
d2 = 3.5 cm
W E

12. Assignment:
Given the following displacement find the resultant
displacement:
d1 = 3.5 cm, 320 north of east
d2 = 2.3 cm, 220 west of north
d3 = 2 cm east
Answer:
dr = 5.5 cm, 420 north of east.

13. Pythagorean Theorem
A plane flying due north at 100 m/s is
blown by a 500 m/s strong wind due east.
What is the plane’s resultant velocity?
Given: v2
v1 = 100 m/s north
v2 = 500 m/s east v1
vr
c2 = a2 + b2 Scale: 1cm = 100 m
vR2 = v1 2 + b2 2
vR2 = (100m/s) 2 + (500m/s) 2
vR = 509.90 m/s

14. To determine the direction of the resultant velocity, use the
equation:
tan Ø = opposite side / adjacent side
tan Ø = 100m/s / 500m/s
= 0.2
tan Ø = 0.2
= 11.310 north of east
vR = 509.90 m/s, 11.310 north of east

15. Kinematics
Motion may be defined as a continuous change of position
with respect to a certain reference point.
Down - Up +

16. Speed and Velocity
Speed is scalar quantity, it represents the rate
of change of displacement.
It represents only the magnitude of velocity.
Most vehicles have a device called a
SPEEDOMETER which measures speed.

17. Average Speed (vs)
The average speed may be defined as the
total distance traveled divided by the time it
took to travel this distance.
distance
vs = d
Average t time
Average speed

18. Average Velocity (v)
Another difference between speed and velocity is
that the magnitude of the average velocity is
calculated in terms of displacement rather than
total distance traveled
distance
average
time
velocity change

19. A car travels a distance of 40km from manila to a
town in Quezon. What is its average speed in
(km/h) if traveling time is from 7:00am to
7:30am? Its average velocity? (km/h)
Average speed
Given:
d= 40 km
t = 7:00am to 7:30 am
= 30 minutes
vs = d / t 1.3km/min x 60 min/h
= 40km / 30 min = 78 km/h
= 1.3 km/min

20. A car travels a distance of 40km from manila to a
town in Quezon. What is its average speed in
(km/h) if traveling time is from 7:00am to
7:30am? Its average velocity? (km/h)
Average velocity
Given:
d= 40 km
t = 7:00am to 7:30 am
= 30 minutes
v =d/t 1.3km/min x 60 min/h
= 40km / 30 min = 78 km/h from Manila
= 1.3 km/min to Quezon

21. Acceleration
Acceleration is a vector quantity since it involves
a change in velocity which is vector.
An increase or decrease in the magnitude of
velocity is called acceleration although the word
deceleration is sometimes used to indicate a
decrease in the magnitude of velocity.
The average acceleration of an object may be
defined as:
Change in velocity
Average acceleration = Elapsed time

22. Initial final velocity
velocity
change
Final time
Average
acceleration initial time

23. What is the average acceleration of the car in the
figure:
0s 1s 2s 3s 4s 5s 6s
Start, v = 0 v1 = 5km/h v2 = 10km/h v3 = 15km/h v4 = 20km/h v5 = 25km/h v6 = 30km/h
Given:
v=0
v0 = 30km/h
t=0 = 30 km/h – 0 / 6 s – 0
t0 = 6 s = 5 km/h/s

24. Energy
Energy is the capacity to do work.
Energy can exists in many forms.
The chemical energy in a battery is
changed into electrical energy that runs
the engine motor.
The engine motor converts the electrical
energy into mechanical energy by
making the other parts of the engine
work to make the car move.

25. Kinetic Energy
Energy possess by any moving object.
The work done by the moving object is
equal to the change in its kinetic energy.
1
KE = mv2
2 Velocity
Kinetic energy mass

26. A 98-kg basketball player runs at a speed of 7
m/s.
a) what is his KE?
Given:
mass = 98-kg
v = 7 m/s
KE = ?
KE = ½ mv2
= (1) (98-kg) (7 m/s)2 / 2
= 2,401 Joules.

27. Potential Energy
Energy possess by any object at rest.
Types of Potential Energy
a) Gravitational Potential Energy
Energy possess by an object
due to its position.
It is determined by the height
GPE = mgh of an object above the earth’s
center of gravity.
mass height
Gravity (9.8m/s2 )

28. Types of Potential Energy
b) Chemical energy
the energy possessed by the
atoms or molecules of a substance and
is released or changed into another
forms when the substance is involved in
a chemical reaction.
this energy depends on the
composition of the substance.

29. Types of Potential Energy
c. Elastic Potential Energy
this is the energy possessed
by an object like a spring or any other
elastic materials due to its condition.
The energy depends on the
average required to compress it and the
distance from its normal length
Elastic Potential Energy = kx2 / 2

30. Law of Conservation of
Energy
“Energy can neither be created nor
destroyed but can only be changed
from one form to another.”
∆KE + ∆PE + ∆(other forms of energy) = 0

31. For example, when the fuel used by a thermal
power plant is burned, its chemical energy is
converted into heat energy.
The heat produced causes the water to boil
and can be converted into steam.
The energy of the steam is transformed in the
steam turbine to mechanical energy.
This energy is changed in the generator to
electrical energy which is distributed to the
consumers.
The electrical energy is converted into light
energy in electrical lamps, sound energy in a
radio, or heat energy in an electric stove.

32. Heat

33. Sources of Heat
A. Natural Sources
a) The Sun
b) The interior of the Earth
B. Artificial Sources
a) Chemical Action
b) Mechanical Action
c) Electrical Energy
d) Nuclear energy

34. Effects of Heat
Heat affects materials in various ways:
1. When substance absorbed heat, its
temperature rises.
2. Solid usually melts or change to liquid state
when heated.
3. Liquid may absorb enough heat when
heated to change to the vapor state.
4. Almost all objects expands when heated.
5. A change in the heat content of a substance
can cause chemical change.
6. Heat causes many changes in bodily
functions of living organisms.

35. Electricity
and
Magnetism

36. Electrical Nature of Matter
When a glass rod is rubbed with silk, some of the free
moving electrons in the glass transfer to the silk cloth.
This breaks the neutral state of both the glass rod and
the silk.
The rod becomes deficient in electrons and is said to be
positively charged.
The silk having gained the electrons lost by the rod, has
an excess of electrons and becomes negatively charged.
In the example given, the number of proton remains the
same throughout.
The object never lose or gain proton.
An object becomes charged with whatever particles it
has in excess.

37. The Coulomb’s Law
The first Law of Electrostatics states that: Like
charges repel and unlike charges attract.
How large is this charge that repels or attracts?
The quantity of charge in the SI system is
expressed in Coulombs ( C ), named after
Charles Augustine de Coulomb.
1 coulomb = 6.25x1018 electrons
q1 q 2 Measured in
F=k Coulomb
9x109 N.m2 /C2 d2 Distance in meter

38. If q1 has a positive charge and q2 a negative
charged, F will therefore be a force of
attraction which will bring the two bodies
closer to each other.
If q1 and q2 are both negative charged
bodies, F will be a force of repulsion which
will make the two charged bodies move
away from each other.

39. The two objects are both negatively charged
with 0.02 C each and are 70 cm apart. What
kind of force exists between them and how
much?
Given:
q1 = q2 = -0.02 C
d = 70 cm
= 0.70 m
k = 9 x 109 N.m2 /C2
Solution:
F = 9 X109 N.m2 /C2
x = (9x109 N.m2 ) (-0.02C) (0.02C) / (0.70m)2
x = 7.3x106 N (force of repulsion)

40. OHM’S LAW
The current flowing through a circuit is directly
proportional to the potential difference and
inversely proportional to the resistance of the
circuit.
The first part of the law may be represented as I
(current)  V (potential difference.
The second law may be expressed as I  I/R
Current or E Potential difference (emf)
the rate of low I= Volts (V)
of electricity
R resistance in Ohms

41. What is the potential difference (emf) in an
electric circuit with a current of 15 amperes
and a resistance of 4.0 ohms?
Given:
I = 15 amperes
R = 4.0 ohms
V= ?
Solution:
I = E/R
15 A = E/ 4.0 Ώ
E = 60 volts (emf)