BASIC SCIENCE JSS2 SECOND TERM LESSON NOTES
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BASIC SCIENCE JSS2 SECOND TERM LESSON NOTES
JSS 2 BASIC SCIENCE SECOND TERM E- NOTE
WORK, ENERGY AND POWER
POTENTIAL AND KINETIC ENERGY
ENERGY TRANSFER WHEN WORK IS DONE
FAMILY LIFE EDUCATION
KINETIC THEORY
KINETIC THEORY
KINETIC THEORY (II)
BOILING AND EVAPORATION
CRUDE OIL AND PETROCHEMICALS
THE HUMAN BODY (SKELETAL SYSTEM AND MOVEMENT)
CALCULATIONS INVOLVING WORK DONE
WORK, ENERGY AND POWER
Week 1
Topic: Work, Energy and Power
Introduction
Work and energy are common concepts we always encounter in our lives on a daily basis. If one does not have energy, one cannot do any work. The stored up energy (potential energy) in our muscular system is converted to kinetic energy. When work and energy are related, they have the same unit of measurement called Joule.
Concepts of Work, Energy and Power
Work
Work is said to be done when a body moves in the direction of the force i.e.
Work = force x distance moved in the direction of the force
W = f x d
Where W = work done,
f = force (F = mass (m) x acceleration of free fall due to gravity (g))
g = 10m/s2
d = distance moved in the direction of the force
Therefore, a force of gravity acting on a 2kg box is 20N; and on a 3kg box is 30N etc.
It is important to note that if the force applied to a body cannot cause motion or displacement, work is not done. For example, if a man was pushed against a wall so much that he began to sweat, but the wall did not move, one cannot say that he has done any work.
BASIC SCIENCE JSS2 SECOND TERM LESSON NOTES
Energy
Since work done is the product of force and distance in the direction of the force, therefore,
F = mg
W = mgh
Where m = mass in kg
g = Acceleration of free fall due to gravity in m/s2
h = distance moved by the force in metres
work done on a 2 kg box = 2 x 10 x 1.5
= 20N x 1.5m
= 30Nm
(Newton metres is the same as joule)
Work done on a 5kg box = 50N x 1.5m
= 75J
The amount of work done on a 5kg box is the greatest, therefore, the 5kg box requires the greatest amount of energy and the 2kg box requires less amount of muscular energy.
Therefore, work done is the measure of the energy used. Then, we can define energy as the ability to do work.
Potential energy is the energy possessed by a body by the virtue of its position and kinetic energy is the energy possessed by a body in motion. These two types of energy are generally called mechanical energy.
Potential energy (W)= mgh
Kinetic Energy (K.E) = ½mv2
Power
Power is defined as the rate of doing work.
P = Work done/ Time
P = W/t
Work done = Fs = mgs
Therefore, P = mgs/t
Where:
P = power in Watts
F = force in Newton
T = time in seconds
M = mass in Kg
g = acceleration of free fall due to gravity
The S.I. unit of power is Joules per second (J/s) or Watts (W)
BASIC SCIENCE JSS2 SECOND TERM LESSON NOTES
Calculation Involving Work Done Per Time (Power)
Example: How much power does a student of 25kg mass who climbed a stair with 20 steps and one step is 15cm high in 30s has? (Assume g = 10m/s2).
Solution:
Distance covered = 20 steps x 15cm
= 300cm = 3m
Power = mgs/t
= 25kg x 10m/s2 x 3m / 30s
= 25 Watts
Energy Transfer: Conversion of Potential Energy to Kinetic Energy
Simple Pendulum
At point A and C, the potential energy is maximum and kinetic energy is zero (because there is no motion at those points). However, at point B the kinetic energy is maximum and potential energy is zero (because the motion is maximum at that point). We can therefore conclude that the potential energy on the bulb at point A has been converted to kinetic energy at point B and the kinetic energy of the bulb at point B has been converted to potential energy at point C.
Furthermore:
Work, Energy and Power
Meaning or work, energy and power
Concept of work, energy and power
Forms of energy (heat, light, kinetic, potential etc.)
Meaning of work, energy and power
Work, energy and power are often used in every day conversation. Work is thought to mean any kind of physical and mental activities, while power is expressed in terms of strength. In science, these terms: work, energy and power have special meanings. For work to be used in science, two things are necessary. There will be force and the force must produce motion. Power on the other hand is the rate at which work is done. Energy is the ability to do work, however the new thing to consider here is thst it is considered in relation to other aspects of our daily lives. In this chapter, the concept of work, energy, power and their calculation will be esplained.
Concept of work, energy and power
Work:
Work is a product of force and distance moved in a given direction, and the quantity of work done is always equal to the quantity of energy put in. In science, work is said to be done when a force can produce movement in a measured direction, i.e. work = force X distance (f X d). Work can simply be defined as the product of distance moved and the force applied in the direction of movement. Note that the useful force is the part of the force, which acts in the direction of movement. If the force is directed in another direction other than that of motion, its component in the direction of motion is the one to use to multiply the distance to obtain the work done.
Generally, for any work done, there must be energy input since energy is the capacity of any system or a body to do work. Both energy and work are measured in units called joules, named after the scientist P. Joules who carried out earlier studies on energy.
Force is that which changes a body’s state of rest or uniform motion in a straight line. It can as well be expressed as: Force = mass X acceleration (F = M X A) where F is force, m is mass and a is acceleration. The unit if force is Newton. If force = mass X action, then Work can be given as: work = mass X acceleration X distance.
This is a simple formula that can be used to calculate work done especially against gravity.
Work done and energy transferred are measured in joules (J). The work done on an object can be calculated if the force and distance moved are known.
A change in momentum happens when a force is applied to an object that is moving or is able to move. The total momentum in an explosion or collision stays the same.
Work, force and distance
You should know, and be able to use, the relationship between work done, force applied and distance moved.
Background
Work and energy are measured in the same unit, the joule (J). When an object is moved by a force, energy is transferred and work is done. But work is not a form of energy – it is one of the ways in which energy can be transferred.
The equation
This equation shows the relationship between work done, force applied and distance moved:
work done (joule, J) = force (newton, N) × distance (metre, m)
The distance involved is the distance moved in the direction of the applied force.
BASIC SCIENCE JSS2 SECOND TERM LESSON NOTES
Power:
Power is also related to the concepts of energy and work. Power is defined as the rate of doing work, i.e. work done divided by time.
Power = Work done
Time taken
The unit of power is watt (w), you can use the formula to solve problems.
Example:
What is power of a child that has done work of 50J in 10 seconds?
Solution:
P = Work = 50 = 5 watts
Time 10
Forms of energy:
Energy has been defined as the capacity to do work. The following are the various forms of energy:
Solar energy
Heat energy
Light energy
Mechanical energy (this is further divided into two: potential energy and kinetic energy)
Electrical energy
Chemical energy
Sound energy
The main source of energy is the sun, it comes as light and heat energy and transformed or changed to other forms. All forms of energy can be transformed or changed from one form to another to another. Electrical energy can be changed to light energy, such as when electricity passes through an electric bulb. Chemical energy can be changed into heat e.g. when you light up a kerosene lamp. The law of conservation of energy explains the transformatory behavior of energy. It states that energy can neither be created nor destroyed but can be changed from one form to another. All forms of energy are measured in Joules.
Potential and Kinetic energy
A stone on the ground does not have energy so long as it is lying on the ground, the stone cannot be seen doing any work. However, if a stone is placed on a table and if it falls off, it can break a lamp on which it falls. The stone here has done some work by virtue of its position. Therefore, when the stone is on the table, it has energy stored up as a result of its position. The type of energy possessed by a body due to its position is called Potential energy. This energy increases as the height of the table increases and it decreases as it falls to the ground. When it reaches the ground, it has zero potential energy. On the other hand, kinetic energy is the energy possessed by a moving body. For example, a moving car, a running man, a falling orange, a fired bullet, a rolling ball, etc. possess kinetic energy.
An object can store energy as the result of its position. For example, the heavy ball of a demolition machine is storing energy when it is held at an elevated position. This stored energy of position is referred to as potential energy. Similarly, a drawn bow is able to store energy as the result of its position. When assuming its usual position (i.e., when not drawn), there is no energy stored in the bow. Yet when its position is altered from its usual equilibrium position, the bow is able to store energy by virtue of its position. This stored energy of position is referred to as potential energy. Potential energy is the stored energy of position possessed by an object.
ASSESSMENT
How much power does a student of 25kg mass who climbed a stair with 20 steps and one step is 15cm high in 30s has? (Assume g = 10m/s2)?
BASIC SCIENCE JSS2 SECOND TERM LESSON NOTES
Week 2
Topic: Potential and Kinetic Energy
POTENTIAL AND KINETIC ENERGY
A stone on the ground does not have any energy so long as it is lying on the ground. The stone cannot be doing any work. However if a stone is placed on a table and it falls off, it can break a lamp on which it falls. The stone here has done some work by virtue of its position. Therefore, when the stone is on the table, it has energy stored up as a result of its position. The type of energy possessed by a body due to its position is called Potential Energy. This energy increases as the height of the table increases and it decreases as it falls towards the ground. When it reaches the ground, it has zero potential energy. Potential energy is the energy that is stored in an object due to its position relative to some zero position. Potential energy, expressed in science as U, is energy that is stored within an object, not in motion but capable of becoming active. An object possesses gravitational potential energy if it is positioned at a height above (or below) the zero height. When you stand at the top of a stairwell you have more potential energy than when you are at the bottom, because the earth can pull you down through the force of gravity, doing work in the process. When you are holding two magnets apart they have more potential energy than when they are close together. If you let them go, they will move toward each other, doing work in the process.
The formula for potential energy depends on the force acting on the two objects. For the gravitational force the formula is P.E. = mgh, where m is the mass in kilograms, g is the acceleration due to gravity (9.8 m / s2 at the surface of the earth) and h is the height in meters. Notice that gravitational potential energy has the same units as kinetic energy, kg m2 / s2. In fact, all energy has the same units, kg m2 / s2, and is measured using the unit Joule (J).
Examples of Potential Energy:
A rock sitting at the edge of a cliff has potential energy. If the rock falls, the potential energy will be converted to kinetic energy.
A stretched spring in a pinball machine has elastic potential energy and can move the steel ball when released.
When a crane swings a wrecking ball up to a certain height, it gains more potential energy and has the ability to crash through buildings.
Tree branches high up in a tree have potential energy because they can fall to the ground.
A stick of dynamite has chemical potential energy that would be released when the activation energy from the fuse comes into contact with the chemicals.
The food we eat has chemical potential energy because as our body digests it, it provides us with energy for basic metabolism.
Kinetic energy is the energy possessed by a moving body. For example, a moving car, a man running, a falling orange, a fired bullet all possess kinetic energy. This is energy possessed by an object in motion. Kinetic energy is directly proportional to the mass of the object and to the square of its velocity: K.E. = 1/2 m v2. If the mass has units of kilograms and the velocity of meters per second, the kinetic energy has units of kilograms-meters squared per second squared. Kinetic energy is usually measured in units of Joules (J); one Joule is equal to 1 kg m2 / s2.
Examples of Kinetic Energy
Flowing flood water can wash away railway lines and bridges.
Water flowing out of a dam can run a turbine to generate electricity.
The wind during a storm can uproot big trees.
The moving wind can run the blades of a wind mill and can be used for producing electricity or for doing some mechanical work.
Example 1
Calculate the work done if a box is pulled by a person with a force of 150N through a distance of 50m.
Work done = force x distance
Force – 150N
Distance – 50m
Work = 150 x 50 = 7500 joules
Example 2
Suppose a body of mass 1kg is lifted through a height of 1m, how much work is done.
The force of gravity on a mass of 1kg is 10 newtons. Distance moved by the force is 1m.
Work done (force x distance) = 10N x 1m (joules)
Example 3
Suppose a ball of mass m kg falls from a height h m to the ground. Calculate the potential energy and the kinetic energy of the ball.
Mass of the ball = m kg
Acceleration due to gravity = gm/s2
Distance of fall = h m
Kinetic energy = mgh joules
Suppose the potential energy of the ball was used up at the time it hits the ground, work done = potential energy = mgh joules
BASIC SCIENCE JSS2 SECOND TERM LESSON NOTES
Example 4
The kinetic energy of a boat is calculated at 36,000 J. If the boat has a mass of 6,000 kg, with what velocity is it moving?
We identify the information given in the problem:
KE = 36,000 J
mass = 6,000 kg
We now place the information into the kinetic energy formula:
KE = 1/2 mv2
36,000 J = 1/2 (6,000 kg) x (v)2
36,000 J/(1/2 x 6,000 kg) = v2
12 = v2
√12 = v2
3.5 = v
Kinetic Energy to Potential Energy
When a body is thrown up, its velocity gradually decreases as it goes up due to the downward pull of earth. As a result, its kinetic energy decreases and its potential energy increases gradually as the body goes up.
This continues until at a certain height, the kinetic energy of the body becomes zero. At this point, the body has maximum potential energy. So, when a body is thrown up, its kinetic energy decreases and the potential energy increases, because its kinetic energy gradually changes into potential energy.
Practice Questions
Calculate the kinetic energy of a moving boat at velocity of 3m/s. The mass of the boat is 60kg.
Suppose a body of mass 30kg is lifted through a height of 6m, and the force exerted on the body is 15N, how much work is done?
A man of 50 kg climbs to the top of a building which is 40 m high. What is the potential energy of the man?
The kinetic energy of a car is found to be 40,000 J. What velocity is the car traveling if its mass is 10,000 kg
Week 4
Topic: Energy Transfer When Work is Done
Work is the force acting on an Object to cause a displacement. Work is done on an object when you transfer energy to that object. If one object transfers (gives) energy to a second object, then the first object does work on the second object.When an object is dropped from above the ground, work is done as the object is pulled to the ground. As the object is falling and work is done, the potential energy of the body is changed to kinetic energy. Work done and energy transferred are measured in joules (J). The work done on an object can be calculated if the force and distance moved are known. A change in momentum happens when a force is applied to an object that is moving or is able to move. In principle, the quantity of potential energy stored in a body is always equal to the kinetic energy produced when the body is released to do work. In order words, when energy changes, for example from potential energy to kinetic energy, there is always an accompanying work done.
Work-Energy Principle –The change in the kinetic energy of an object is equal to the net work done on the object.
Assessment
A force of 20N pushing an object 5 meters in the direction of the force. How much work is done?
The work done on an object is 5 Kilo joules and the object moved a distance of 800cm. Calculate the force acting on the object.
Answers
Workdone = Force x distance
20N x 5m = 100Nm or joulesWorkdone = Force x distance
Force = Workdone/distance
work done = 5 kilo joule convert to joules = 5 x 1000 = 5000 joules
distance = 800 cm.
100cm = 1m
800 cm = 8m
Force = 5000/8 = 625N
Further discussion on Energy transfer when work is done
If you apply a force over a given distance – you have done work. Work = Change in Energy. If an object’s kinetic energy or gravitational potential energy changes, then work is done. The force can act in the same direction of motion. Or, the force can act against the motion. (Drag and friction do that.) Forces can act when objects touch.
In general, the energy transferred depends on the amount of force and the distance over which that force is exerted.
If the man pushes the rock in the direction of the force, he has done work. If the rock rolls back and pushes him, then the rock does work on the man.
No work: If the net force is perpendicular to the motion then no work is done. If you push on an object and it doesn’t move, then no work is done. If an object’s kinetic energy doesn’t change, then no work is done.
Another Equation for Calculating Work:
Work = Mass * Gravity * Height and is measured in Joules. Imagine you find a 2 -Kg book on the floor and lift it 0.75 meters and put it on a table. Remember, that “force” is simply a push or a pull.
Work = Mass X Gravity X Height
= 2 X 10 X 0.75
= 14.7 Joules
Energy is defined as the ability to do work. If you can measure how much work an object does, or how much heat is exchanged, you can determine the amount of energy that is in a system. As with work, energy is also measured in Joules. Energy is not created nor destroyed according to the Law of Conservation of Energy. Energy only changes form. It is transformed from one kind of energy to another. In fact, the energy that makes your body work can be traced back to the sun. Solar energy is transformed to chemical energy in the plants. We get chemical energy from the plants and animals we eat.
In science, we say that work is done on an object when you transfer energy to that object. If you out energy into an object, then you do work on that object (mass). If a first object is the agent that gives energy to a second object, then the first object does work on the second object. The energy goes from the first object into the second object. At first we will say that if an object is standing still and you get it moving, then you have put energy into that object. The object has kinetic energy as a result of your work. You pushed it through a displacement, you did a work on the object.
For example, a golfer uses a club and gets the stationary golf ball moving when s/he hits the ball. The club works on the golf ball as it strikes the ball. Energy leaves the club and enters the ball, this is a transfer of energy. Thus we say that the club did work on the ball, and before the ball was struck, the golfer did work on the club. The club was initially standing still, and the golfer got it moving when he or she swung the club.
So, the golfer does work on the club, transferring energy into the club, making it move. The club does work on the ball, transferring energy into the ball, getting it moving.
Questions
How much work is done if a force of 20N is used to displace an object 3m?
Work done = Force X distance
W = 20N X 3m = 60Nm or 60 Joules
A force of 15.73N acts on an object over a displacement of 16.93m. The force and displacement are in the same direction. How much work does the force do on the object?
Work done = Force X distance
W = 15.73N X 16.93m = 266.31J
How much work is done by a force of 25N that operates over a displacement of 6.2m?
Work done = Force X distance
W = F X D = 25 X 6.2 = 155J
BASIC SCIENCE JSS2 SECOND TERM LESSON NOTES
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