00:00 Hello students, my name is Uche Ugo, the subject is basic science and I will be taking

00:20 the topic work energy and power. At the end of this lesson, I would expect each student to have achieved several objectives.

00:33 The first objective being to be able to define work, energy and power. The second specific objective I expect each student to achieve is to be able to list and describe the various forms of energy.

00:50 Then the third one is to be able to explain the concepts of potential kinetic energy which are the two forms of mechanical energy.

01:02 Then the last objective is to be able to solve calculation problems that arise from problems involving work done by a body.

01:16 Introduction. If you look at the screen, you see a yoga mat lifting a rod with two buckets at each end.

01:28 Now, this particular activity is called work done. Now, for this particular yoga mat to have been able to lift this bucket, it requires a force, a force is needed to lift this particular bucket.

01:44 Now, for that force to act, it means that this person must have an energy which he has told that allows him this force to act on that rod and this bucket is lifted.

02:01 What does it mean? It means that a particular form of energy or the body must possess energy to supply force that is needed to do work.

02:13 Now, from one item body or person to another, the rate at which work is carried out differs.

02:23 So how fast you are able to do work compared to another is different and that term is referred to as power.

02:31 So the power of a body or a rate at which a body executes its own duty or work differs from another.

02:40 So we will be looking at the meaning of work energy and power, the concept and the various forms of energy that exists.

02:49 Also, we will be looking at the mechanical energy which is kinetic and potential. They will look at light and heat energy on the various forms of energy.

03:01 Now, what is work?

03:04 What can be defined as the combination or product of the force acting on the body and the distance it covers, which is force times distance covered.

03:16 Now, this force acts or moves in a direction which is in the direction of the object which is being acted upon.

03:30 Now, there is a condition for that distance not to be included in calculating the work done by a body.

03:39 In a case where the force is acting perpendicularly to the distance and not in the same direction, we do not consider distance.

03:49 But this particular calculation is different where an angle is formed.

03:55 Now, you should note something. For work to be done, a force must be applied and there must be a displacement.

04:03 This displacement is talking about the distance covered in any given direction. And like I said, there is an exception when the force acts perpendicularly to the direction of its force.

04:17 An example is a man who is pushing a barrel. This man is exacting a particular force.

04:24 And you find that the force he is exacting is in the same direction which the object which is the wee barrel. He is doing the work in the same direction.

04:34 He is handling the holding the handle of the wee barrel, pushing the force in the direction in which the wee barrel is moving.

04:42 So, the force is there and the distance in a direction gives you the work done for that particular man.

04:52 And the formula is seen as force times distance. And it is named by a particular man known as James Prescott Joe.

05:02 James Prescott Joe was a scientist who carried out a lot of research in field of energy and work done.

05:11 His numerous experiments made the science committee to recognize the units of work done or energy as Joe's, which is named after his surname.

05:24 Now, energy as we all know is the ability to do or carry out a work. Now, energy cannot be destroyed.

05:34 Energy can be transferred from one object to another. It can be transferred from one state to another.

05:43 What do I mean? Energy can be transferred from mechanical to heat, heat to mechanical, from light to heat, light to electrical or whatever.

05:54 And it is also measured in Joe's meaning it has the same units as work done. And the main source of energy is the solar energy from the sun.

06:04 Then what is power? Like I said earlier on, different objects carry out work or different mechanism carry out work at different rates.

06:14 Now, the rates at which work is carried out is what we refer to as energy. We also say energy can be defined as the amount of work done, which is divided by the total time taken to execute that work.

06:28 It is expressed in terms of watts. So the formula is work done divided by time, that is W over C.

06:41 Now, there are different forms of energy that is energy exists in different forms.

06:48 The first one is heat energy. This particular type of energy is released due to the movement within the tiny particles of atoms of an element.

07:01 So when atoms move, whether they are moving in solid, liquid or geothermal state, heat is released.

07:10 Now, this particular heat energy can be transferred from one object to another, as you will see in the topic called thermal energy.

07:22 An example of this process or experiment is the steam, which is used in steam engines to allow them to function.

07:33 Now, how does this steam propel the steam engines? The steam hits off the piston of the steam engine. The piston moves in the front and back movement, which is called a connecting rod.

07:48 Now, this movement propels the steam engines to function and carry out these duties.

07:55 Now, we have the mechanical energy, which is divided into the potential and kinetic energy.

08:03 Now, light energy is the type of energy that allows an object to absorb light, which falls on the human eyes.

08:14 So, the principle in which human beings can observe something, for example, I'm staring at the screen and I can see what is written on the screen because light falls on my eyes and reflects directly on the screen, allowing my retina of my eyes to fully see the colors on the screen.

08:36 Now, this is very useful in cameras, in what we call photography, because the light is used in a part of the camera called the light meter.

08:50 Now, we have the solar energy, which is the major source of energy. The solar energy comes from the sun and it can be converted into various forms into heat energy, which is the thermal energy.

09:04 It can also be converted into electrical energy, as we see in our source of light, like our solar panel and our inverters we use in our homes.

09:18 Sound energy, this one works on the principle of wave movement. The wave particles move in form of sound through mediums like air or water and they move to generate another form of energy at a different point.

09:37 For example, your microphones, when you place your mouth on the microphone, you release sound energy, the sound energy which you release moves through the microphone and direct to the speakers.

09:52 You prove what we call a teen plate. We also have chemical energy. Chemical energies are stored in bones. We have covalent and ionic bones.

10:03 Now, these kind of energies exist in atomic, molecular or element states. Now, they are released when chemical reactions take place.

10:17 These chemical reactions involve reactions like neutralization, reaction that's reaction between an acid and a base.

10:25 Now, this kind of energy can be stored in objects such as batteries and fuels. All these form of energies are said to be incompatible, meaning they can easily be converted from one form to another.

10:42 Remember, I said energy cannot be destroyed. Now, if you look at the diagram before you on the screen, you see a young man holding a catapult.

10:54 The energy stored in this particular catapult is referred to as potential energy. Why?

11:00 Being that the catapult is not being set into motion. It is still standing still. So, it has stored an energy in form of potential energy.

11:11 So, what is potential energy? This is the energy stored in a stagnant body, a body that is at rest or stationary.

11:21 Now, this particular energy can be found in objects that are not moving or in a particular position.

11:31 Now, it is given by MGH, where M is the mass of the body. Now, G refers to acceleration, but this small G you see is acceleration due to gravitational force.

11:47 And its value is about 9.8 m/s square, but it can be approximated to 10 m/s square. Now, the H is the height of the body.

12:02 So, these three units come together to give you U, which is referred to as gravitational energy or potential energy.

12:12 The acceleration due to gravity, like I said, can be measured in meter/s square or Newton/kg.

12:22 That is, the force of the body over the mass of the body. Whereas, the distance covered by the object is usually measured in kilometers or meters.

12:36 Let's take an example. The question says, find the potential energy of an object that has mass of 20 kg and it is placed on a table that has a height of 8 m.

12:51 And we are giving the acceleration due to gravity to be approximated to about 10 Newton/kg.

12:58 Now, solution. We know that potential energy U or gravitational energy is obtained by multiplying the mass of the body, the acceleration due to gravity, which is your 10 Newton/kg and the height covered by that body.

13:19 So, our potential energy will be 20 kg, which is the mass of the body multiplied by the height, which is about 8 m and the acceleration due to gravity, which is 10 Newton/kg.

13:37 We obtained 1,600 joules, which is the unit of our energy. So, the energy or the potential energy stored by this body is around 1,600 joules.

13:54 Now, let's look at kinetic energy. This is the second type of mechanical energy and it is unlike the potential energy, it is the type of energy stored for a body that is in motion.

14:07 Now, when a body moves, there is an energy it possesses. That energy is referred to as kinetic energy and the level of kinetic energy a body possesses depends on two factors, which are its mass and the velocity or speed at which it is moving.

14:28 Now, the kinetic energy is denoted as KE. If you look at this system, you see the rotation, the wheel rotation, generating energy.

14:47 This is electrical converted to mechanical. This point is inserted into the socket. It causes the wheel to spin, generating a form of mechanical energy and form of kinetic energy.

15:04 And it is obtained by calculating half of the total mass of the object multiplied by the square of its velocity, that is, half MV square.

15:17 So, M is the mass of the object and V is the velocity of the object. So, we have an example.

15:26 A boy of mass 10 kg is moving at a constant velocity of 15 meters per second, calculate his kinetic energy. This is very simple.

15:37 Kinetic energy equals half MV square. So, we have one over 2 times the mass, which is 10 multiplied by the square of its velocity, which is 15 square.

15:51 So, half times 10 times 15 square gives us 225 multiplied by the 2, which is the denominator of the half by 10. You have 5 multiplied by the 225.

16:05 Then the energy possessed by this body is about 1,125 joules. So, the body has a kinetic or moving energy of 1,125 joules.

16:21 Let's look at some calculations involving work done by a body. The first example says, a boy of mass 20 kg climbs a staircase of about 8 meters and we are asked to calculate the work done by the body.

16:39 Note that acceleration due to gravity given to us is 10 newton per kilogram.

16:46 Now, work done is gotten by multiplying the force and the distance of the body and the force of the body is gotten by multiplying the mass of the body and the acceleration given.

17:02 Now, we know that the mass of the body is 20 kg and the acceleration due to gravity given to us is 10 newton per kilogram.

17:12 So, when you multiply the 20 and the 10, we get 200 as our force. Now, to get our work done, multiply the force and the distance.

17:22 So, 20 times 10 multiplied by the distance of the staircase, which is 8 meters, gives us the total work done, which is 1,600 joules.

17:34 The second question says, a boy of mass 10 kg runs up a staircase having a height of 3.00 meters. Find the work done against gravity.

17:50 And we are giving an acceleration due to gravity, same as the first question, 10 meters per second squared. So, look at the solution.

18:00 We know that work done is mass times acceleration due to gravity times the distance, which is the height of the staircase.

18:10 So, we have our mass 10 kg, we have our acceleration due to gravity as 10, we have our height as 3.

18:20 So, we multiply 10 with 10, then with the 3, then we have a total work done of about 300 joules.

18:32 The third question says, calculate the work done by a body of weight 200 newtons, which moves through a distance of 12 meters.

18:43 If you look at the question, you see that we have given a weight, which is in form of the force that is used to act upon the body 200 newtons.

18:55 And we are giving a distance of 12 meters. And we know that work done is the product of force and distance.

19:03 So, we simply multiply our force 200 newtons by a distance 12 meters, which gives us a total work done or energy of 2400 joules.

19:16 These are some questions to test your knowledge on the teaching of today.

19:22 Number one says, what is the condition for a body to be able to work?

19:28 The second question says, when is it possible for a body to do work while covering a particular distance in a given direction?

19:39 The third question says, why is the SI unit of energy called joules?

19:47 The fourth question says, mention the factors that determine the amount of kinetic energy that a moving body possesses.

19:57 Then the fifth question says, if a tricycle of mass 15 kg moves with an acceleration of 17 meter per second square, calculate the force with which it moves.

20:14 Thanks for watching. My name is Uche Ugo, till next class.