Notes from the Observatory textbook. Summarizes what the students should know.

1. Chapter 3
Different Forms of
Energy

2. A Quick Review
• What are the following?
1. Energy transformation
2. Forms of energy
1. Chemical
2. Thermal
3. Mechanical
4. radiation
3. Temperature
4. Mass

3. 1 – What is energy?
• Energy occurs in many forms and from many
sources.
• See Table 3.1 on page 70
• Energy is the ability to do work or effect
change.
• The International System of Union (SI)
expresses energy in joules (J)
1 J = 1N/m

5. 1.1 – The Law of Conservation of
Energy
• Energy Transfer is the movement of energy
from one place to another.
• Energy Transformation is the changing of
energy from one form to another.
• Law of Conservation of Energy: Energy can be
neither created nor destroyed; it can only be
transferred or transformed.

6. 1.2 – Energy Efficiency
• Energy can be changed from one form to
another.
• Energy conversion rarely results in all of the
energy being converted into useful energy.
• Energy efficiency is the percentage of energy
consumed by a machine or system that was
transformed into useful energy.
Energy efficiency = amount of useful energy X 100%
amount of energy consumed

7. Only 12% of the chemical energy from gasoline
is actually used by the wheels to make the car move

8. 1.3 Thermal Energy
• Random movement of all the microscopic
particles in a substance.
• Factors Affecting Thermal Energy (Fig. 3.4)
Factor Factor variation Results
Number of particles More particles Increased thermal energy
Fewer particles Reduced thermal energy
Temperature Higher temperature Increased thermal energy
Lower temperature Reduced thermal energy

9. • Thermal energy is the energy contained in a
substance, determined by the number of
particles in the substance and the temperature
• How can we determine the number of particles?
– Find the mass!!
• Heat is the transfer of the thermal energy
between two environments with different
temperatures.
– Heat always moves from the warmer environment to
the cooler environment

10. • The relationship between heat and thermal
energy is expressed by this equation
Q=ΔEt
Q = the heat (in J)
ΔEt= the variation in thermal energy (in J)

11. • How are heat and temperature different?
• Temperature is a measure of the degree of
agitation of the particles of a substance
• Heat depends on the degree of agitation and
the mass of the substance

12. Specific Heat
• Oil heats faster than water. Why?
• Water has a specific heat of 4.18 J/g0C
• Vegetable oil has a specific heat of 2.00 J/g0C
• Oil heats easier than water – gets warm faster
with the same amount of heat applied.
• What does this really mean???

13. What it means…
• To raise the temperature of 1 g of water by 1
0C requires 4.185 J of energy.
• To raise the temperature of 1 g of oil by 1 oC
requires 2.000 J of energy.
• It requires 2.09 times as many joules to raise
the temperature of the water .

14. Substance Specific Heat Capacity
(J/g0C)
H2 gas 14.267
He gas 5.30
H2O (l) 4.184
Ethyl alcohol 2.460
Vegetable oil 2.000
Air 1.020
Concrete 0.88
sand 0.290
Silver 0.240
Gold 0.129

15. • The specific heat of hydrogen (H2) is 14.26
• The specific heat of air is 1.02
• Is air or hydrogen easier to warm up?
• Air by a factor of 14!!!!
• Hydrogen requires 14 X as many joules to heat
the same amount!!

16. Why does sand feel so hot on the
beach on a warm summer day?
• Air - 1.020
• Sand - 0.290
• Do the math:
1.020/0.290
= 3.52
Air requires 3.5 times as many joules of energy to
heat up.
A smaller specific heat capacity means the
substance requires less energy to heat it up.

17. Substance Specific Heat Capacity
(J/g0C)
H2 gas 14.267
He gas 5.30
H2O (l) 4.184
Ethyl alcohol 2.460
Vegetable oil 2.000
Air 1.020
Concrete 0.88
sand 0.290
Silver 0.240
Gold 0.129

18. • Which substance on the list heats the easiest?
• Gold!!!

19. • Checkup page 99
• Do questions 1 to 6
• Read pages 79 – 87 - Motion and Forces

20. • When two different substances are heated,
their temperature increases but not
necessarily at the same rate.
• The specific heat capacity corresponds to the
amount of thermal energy required to raise
the temperature of one gram of a substance
one degree Celcius.
• The heat absorbed or released by a given
substance can be calculated!!!

21. Q = mcΔT
• Q = the heat present in the substance
• m = the mass ( g)
• c = the specific heat capacity of the substance
(J/gοC)
• ΔT = the change in temperature (οC)
• ΔT = Tf –Ti
– Tf is the final temperature and Ti is the initial temperature

22. A beaker containing 100 g of water
is heated from 20oC to 44 0C.
Q = 100 x 4.19 x 22
= 10 056 J
A beaker containing 100 g of
vegetable oil is heated from 20oC to
44 0C.
Q = 100 x 2.00 x 22
= 4 800 J
A beaker containing 200 g of water
is heated from 20oC to 44 0C.
Q = 200 x 4.19 x 22
= 20 112 J
A beaker containing 100 g of water
is cooled from 20oC to 44 0C.
Q = 100 x 4.19 x -22
= -10 056 J
Remember that the ΔT = Tf – Ti, which in the first 4 examples is 44-20 = 24
There is an error in your textbook!!!! Find the error.

23. 1.4 – Kinetic Energy
• Kinetic energy is the energy an object posses
due to its motion.
• Energy of motion!!!!
• Items at rest have no kinetic energy!!!
• The amount of kinetic energy depends on two
variables:
1. Mass
2. Velocity

24. Ek = ½mv2
Ek = the kinetic energy of the object (J)
m = mass of the object (kg)
v = velocity of the object (m/s)
• A car weighing 2500 kg travels at 50 km/h
(about 14 m/2)
Ek = ½ mv2
½ x 2500 kg x (14 m/s )2
= 245 000 J

25. • A car weighing 2500 kg travels at 100 km/h (about 28 m/s).
Ek = ½ x 2500 x (28)2
= 980 000 J
• A minivan weighing 5000 kg travels at 50 km/h ( 14 m/s).
Ek = ½ x 5000 x (14)2
= 490 000 J

26. 2 – Motion and Forces
2.1 - Motion
• The main variables to describe the motion of
an object are:
1. Speed (velocity)
2. Distance travelled
3. Travelling time
• There is a mathematical relationship
between these values:
v = d
Δt
v= velocity (m/s)
d= distanced travelled (m)
Δt = travelling time (s)

27. Finding the velocity using a graph
• A position-time graph shows us the time (s)
and the distance (m).
• The steeper the slope the greater the velocity
0
2
4
6
8
10
12
14
0 2 4 6
Average Velocity
Average Velocity
Distance
(m)
Time (s)
V = d/Δt
V = 6m/2s
V = 3 m/s

28. 2.2 Forces and Change
• Pushing or pulling in object is exerting a force
on the object.
• A force is an action that can change the
motion of an object, or deform the object, by
pushing or pulling on it.
• A force is always exerted by one body on
another, and in one direction.

29. • The force can be represented graphically with an
arrow.
• The following 4 points must be taken into account
1. The horizontal or vertical line of action is represented
by a straight (dotted) line
2. The direction of the applied force is represented by
the arrow
3. The magnitude (size) of the force is represented by
the length of the arrow.
4. The point of application of the force corresponds to
the starting point of the arrow.

30. 350
20 N
A simple diagram to show the same information

31. 350
350
20 N 10 N
Shows two different forces – different lengths for the lines.
The angle is very important for determining the force.

32. • Force is measured in Newtons (N)
• A Newton is the force required to make a one
kilogram object accelerate at a rate of 1 m/s2.

33. A force can change the motion of an object in different
ways:
1. A force acts on a stationary object by giving it a certain
velocity. A force can increase the velocity of an object
already in motion if the force is exerted in the same
direction as the motion – causes the object to accelerate.
2. A force can reduce the velocity of an object if the force is
applied in the opposite direction to the motion. The
object may slow down or stop. This is deceleration or
negative acceleration.
3. A force can also modify the trajectory of an object, modify
the course. This happens when a force is applied on one
side of a moving object. This is also a form of acceleration.

34. 2.3 Types of Forces
• There are four main categories:
1. Gravitational force
2. Electromagnetic force
3. Strong nuclear forces
4. Weak nuclear forces
• These forces can act across a distance and
direct contact between two bodies is not
required!

35. Gravitational Force
• This is the force of attraction between all objects
as a result of their masses and the distance
between the objects.
• Heavier objects have a stronger gravitational
force.
• Objects that are farther away have weaker
gravitational forces – weak attraction.
• The Earth has a large mass and is close by so it
has a strong gravitational pull on objects on the
surface of the Earth

36. • The gravitational pull on
all objects, on the surface
of the Earth is 9.8 m/s2.
• Gravitational pull is
toward the center of the
Earth so the farther you
move from the center of
the Earth, the smaller the
gravitational pull exerted
on an object.

37. • Gravitational force explains falling objects,
celestial bodies and tides.
– The force of gravitational pull exerted by the
moon affects tides
• Discussed in detail in Chapter 7

38. The relationship between mass and weight!!
• In science, they do not mean the same thing.
• Mass is a measure of the quantity of matter in an
object.
• Weight is a measure of the gravitational force
acting on an object.
– w = Fg = mg
w= weight in N
Fg = gravitational force in N
m = mass in kg
g = gravitational field intensity in N/kg

39. • Example: If you have a mass of 60 kg on
the surface of the Earth you will weigh 60
x 9.8 =588 N
• On the moon: 60 x 1.67 = 100 N
• Venus: 60 x 8.62 = 517 N
• Jupiter: 60 x 25.87 = 1552 N

40. Electromagnetic Force
• A force of attraction or repulsion between two objects
with electrical charges or with magnetic poles.
• Responsible for the bonds between atoms in a
molecule.
• Also responsible for muscle tension, magnetic
phenomena, and the movement of electric current.
• Electromagnetic forces are also responsible for contact
forces.
• These forces are the result of direct contact with an
object

41. • The table resists the pressure of the book
by opposing it with an electromagnetic
contact force equal to the weight of the
book.

42. The force of friction
• Friction is a form of contact force.
• Wears machine parts out but also allows us to
walk and do many other every day things.
• Air resistance is also a force of friction.
• Friction occurs between two objects whose
surfaces are not perfectly smooth, when they
come into contact.
• Friction must be overcome in order for an
object to be in motion.

43. • Friction is a force that prevents two objects from
slipping over each other when they come into
contact.
• Friction depends on two factors
1. The nature of the surfaces in contact – rougher
surfaces = greater friction
2. The intensity of the pressure of each surface on
the other - higher pressure = greater friction
• Slip is the opposite of friction

44. Strong and weak nuclear forces
• These act within the nucleus of the atom
• The force is non-existent outside of the
nucleus.
• Strong nuclear force:
– High intensity force of attraction that holds
protons and neutrons together
• Weak nuclear forces:
– Low intensity force of attraction - radiation

45. 2.4 – The Equilibrium of Two Forces
• Every object is constantly to at least one force:
– GRAVITY
• Most objects are subjected to several forces at
the same time.
• The resultant force (net force) is a virtual
force whose action is equal to the
combination of all the forces applied
simultaneously to an object.

46. • When the resultant force is zero, the object is at
equilibrium.
• The motion of the object remains constant.

47. 3 – Forces in Fluids
• What is pressure?
– Force/area
• What is density?
– Mass/volume
• Pressure is the force applied perpendicular to
an object per unit of surface area.
• Pressure is measured in Pascals (Pa)

48. P = F
1 Pa = 1 N
A
P = pressure in Pa
F = force perpendicular to the surface in N
A = surface area subjected to the force in m2
1 m2

49. • Pressure in a liquid depends on two factors:
1. The depth
2. The density
Figure 3.28
Factor Factor Variation Result
Depth Increased depth in the liquid Increased pressure
Reduced depth in the liquid Reduced pressure
Density Higher liquid density Higher pressure
Lower liquid density Lower pressure

50. • Pressure in a gas depends on the number of
collisions between the gas particles.
• More collisions = greater pressure.
• There are 3 factors that influence the number
of collisions:
1. Temperature
2. Volume
3. Number of particles

51. Figure 3.31 Factors influencing pressure in a gas
Factor Factor Variation Result
Temperature Higher gas temperature Increased pressure
Lower gas temperature Reduced pressure
Volume Higher gas volume Reduced pressure
Lower gas volume Increased pressure
Number of particles Higher number of particles Increased pressure
Lower number of particles Reduced pressure

52. 3.2 – Pascal’s Principle
• He was a French physicist and mathematician.
• Pascal’s Principle states that an increase in the
pressure of an enclosed fluid is transmitted
uniformly in all directions.
• This principle applies to water pistols and
hydraulic breaks!

53. • In the situation,
force is transmitted
from one point to
another, making it
possible to do work
across a distance

54. • In this situation the applied
force is amplified.
The small downward force
result in a strong upward force

55. 3.3 – Archimedes’ Principle
• When dropped in a liquid, an object can float,
remain suspended at a certain depth or sink.
• Archimedes discovered that the volume of a solid
can be determined by measuring the volume of
water it displaces.
• Archimedes also knew that pressure in a liquid
increases as the depth increases, creating an
upward force called buoyancy.
• The magnitude of the buoyant force is equal to
the weight of the fluid displaced by the immersed
object.

56. • Archimedes’ Principle states
that an object immersed in a
fluid is subjected to a buoyant
force equal to the weight of
the fluid displaced by the
object.
• Air is a fluid and acts the same
way but the weight of the
displaced air is usually much
less than the weight of the
object so very few objects are
suspended in the air.

57. Three possible situations:
• Buoyant force (Fb) is weaker than the force of
gravity (Fg) Fb<Fg - results in a downward
force and the object sinks
• Fb=Fg - resultant force is zero so the object
maintains the same depth
• Fb>Fg - resultant force is directed upward
and the object rises to the surface

58. Figure 3.35 – Determining the buoyant force
• The anchor has a volume of 2 L and a weight of
150 L. The volume of water displaced by the
anchor is 2L. The weight of the water displaced is
20 N therefore the buoyant force is also 20 N. 20
N is less than 150 N so the anchor sinks.
• Another way to think about it!
• Water has a density of 1.0 g/mL. To find the
density of an object use the formula p = m/V.
• The anchor has a mass of the anchor is 1000o g
and it has a volume of 2 L = 2000 mL. Density =
10000g/2000 mL = 5.0 g/mL
• The density of the anchor is greater than the
density of water so the anchor will sink.

59. Ships are designed to displace a large volume of water.

60. When the ballast tanks are
filled with water, the weight
of the boat increases and it
sinks. To make it rise, they
empty the water out of the
ballast tanks. As the boat
becomes lighter it rises.

61. 3.4 – Bernoulli’s Principle
• Bernoulli’s Principle states that the higher the
speed of a fluid, the lower its pressure, and vice
versa.
• This principle explains how planes fly.
• The air particles travelling over the curved upper
wing surface must go faster to keep up – it has to
go farther . The increased speed of the particles
creates lower pressure on top. The pressure on
the bottom is greater, so it wants to lift the
plane.

62. Making Bernoulli's
Principle Fun

63. • The shower causes air displacement,
inside the shower now has a lower
pressure so the curtain moves in!!
• The increase in the pressure do to the
tilt of your hand can increase or
decrease the pressure forced on the
bottom of your hand is Newton's third
law.