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The Law of the Conservation of Energy
The Law of the Conservation of Energy
The Law of the Conservation of Energy states that Energy can not be created or destroyed, it can only transfer or transform.
Transfer = go from one place to another
Transform = go from one form to another (like the cartoon transformers, robots in disguise) eg. from electrical to light in your monitor
The Law of the Conservation of Energy means that all the Energy in the Universe is Fixed.
It is the same now as it was in the second after the Big Bang, it has been the same ever since, and it will still be the same at the end of the universe.
Einstien's equation E=mc2 makes it slightly easier to understand Energy.
He effectively says that mass and energy are the same thing; mass is energy slowed down. Mass is condensed Energy.
So, if you can break mass down atoms down, you get energy = Nuclear Energy.
This is what happens in the Sun = 4 Hydrogen atoms are fused to make 1 helium atom, but its mass is slightly less than the mass of 4 Hydrogen atoms, this lost mass is now energy moving at the speed of light - it is light.
This light then powers life on our planet through photosynthesis. We eat things, we move (kinetic) we are warm bodies (heat) we talk (sound) so we transform the lost mass of the universe (nuclear energy, then light energy, then chemical energy) into other forms of energy.
When we are alive we are always turning some of our energy into heat energy. If we exercise, go for a run, we get sweaty - because we are turning more of this energy into heat energy. When we pass away our bodies go cold.
All energy ends up as heat energy, radiating off into the universe
Watch the Clip to the side that says "When a physics teacher knows his stuff - this shows the consequence of friction causing energy in the system turning into heat energy
The energy In
Work = Force x distance
Work = weight force x distance
(weight = gravity x mass)
(vertical distance = height)
So
Force x distance = mass x gravity x height
Work = GPE
Energy out
Kinetic Energy + Heat Energy + Sound Energy
Professor Dave to the side explains this very well
Have a play with Systems Below
tick Energy Symbols.
What does it show you?
Remember to feed your cyclist - why?
This is the Law of the Conservation of energy: Energy can not be created or destroyed, it just changes forms (Transforms) or moves places (Transfers)
The amount of energy in the universe is NOT Infinite
Rather, there is only a finite amount of energy in the universe
Energy cannot be created
Energy cannot be destroyed
Rather, it just changes forms
Forever changing
But what is Energy?
It is surprisingly hard to define - but I see it as being, the ability to do stuff
Without energy the universe would be like a dark, frozen photograph. Everything frozen, nothing moving, no life, no heat, and no anything, as matter is condensed energy.
Energy, moreover the transfers and transformations of energy allow everything to happen.........everything! Light, a thought, an emotion, the moon orbiting the earth, the light and heat of the sun..... everything!
So, if we go through a brief history of the energy you are using to read this, it will look like:
Big bang, nuclear fusion, light energy , photosynthesis, chemical potential energy in grass, chemical potential energy in sheep, chemical potential energy in you, kinetic energy in the muscles of your eyes, heat energy
Energy keeps changing forms, or Transforming
Energy can transform from and to any of the types showing in the images below
Energy can be stored Potential Energy, such as Chemical PE, Nuclear PE, Gravitational PE or Elastic PE
Energy can be moving, like Light Energy, Thermal, Sound, Electrical or Kinetic
Heat Energy Escapes
Heat Energy Escapes
Why does a skateboard eventually stop when launched from the top of a Vert or Halfpipe ramp?
Imagine it going from the top where it has GPE, down where it is decreasing its GPE and increasing its EK as it speeds up, then back up the other side, where its GPE increases as it goes up the other side but it slows down so EK decreases. Then it gets up as high as it can, then it stops for a nanosecond, it now has no Ek just GPE - but not as much GPE as it started with? Why not?
GPE = EK + Heat = GPE + Heat Energy = EK + Heat Energy = GPE + Heat = EK + Heat
But Heat Energy escapes the system
Have a play at the Energy Skate Park PHET below
Turn Friction on and off - what happens?
Turn on the Energy Graphs - What do they tell you?
Energy Efficiency
Energy Efficiency
Heat is always lost from a system.
Often you cannot use this energy. For example a human running - the energy used to make you warmer is effectively unusable energy. (on the other hand, shivering when you are cold is useful energy.
Another example is a car engine - it gets hot on your drive to school. This heat is again wasted energy. The energy you wanted from the burning of your petrol was Kinetic Energy to move the car forward. You add oil to the engine to reduce friction. This makes it more efficient.
To calculate the energy efficiency of the engine you take how much energy you get out that you wanted OUT of the system (Kinetic Energy) and divide it by the energy going IN to the system (Chemical potential energy in the petrol) then x100 to get a percentage.
Energy Graphs
Energy Graphs
Friction turns Kinetic Energy into Heat Energy
This is also why your brakes get hot and your tires smoke if you stop really fast in a car - the friction between the brake pads and the brake disc, and the friction between the tires and the road.
Actually the only reason you ever stop - in your car - on your Mountain bike - is because of heat energy lost due to friction. Try stopping your bike or car on ice - no friction means no heat energy lost which means no stop.
If we put a person on a Skateboard ramp, and look at the energy graph, we will see that the Total Energy is equal to the Gravitational Potential energy
Then as they go down the ramp, we see that the potential decreases and the kinetic increases
At the bottom of the ramp, it is all Kinetic and no more potential - BUT - the kinetic does not equal the total. Why not?
Have a look at Thermal Energy
Due to Friction in the skateboard wheel bearings
Friction with the air molecules
Friction is the interaction of 2 or more substances moving past each other - this ALWAYS generates heat energy
You can use grease and oil and lycra to decrease the friction, but there will always be some
As long as there is Friction, there will be energy transformed into Heat Energy
This heat energy radiates out into the universe
Each time she goes up and down the ramp what happens to the height she reaches?
As she goes up and down the ramp more and more times her height each time decreases.
This is because less of the total energy is able to be turned back into potential energy each time, as every time heat energy is also created, thus reducing the total usable energy.
This continues until she eventually comes to a stop
At the stop point, all of the Initial Energy as been Transformed into Heat energy
Perpetual Motion
Perpetual Motion
Because there will always be some energy lost from the system as heat energy due to friction of the parts, how do perpetual energy machines that you see on tictok etc work?
Have a watch of the Transparent Youtube above
Joules
Joules
Without Energy everything stops
You need energy to move
When your car runs out of energy, it stops moving
When your phone runs out of energy, you stop scrolling
When your laptop runs out of energy, electrons stop moving
When a tree runs out of energy, transpiration stops, the tree falls down.
When you run out of energy, you stop moving and are buried
Without energy, everything stops.
So energy is needed for things to move
Energy can be quantified - given numbers
My PC uses more energy than my Laptop
A branch will burn for longer than a twig
It takes more energy to run to school than to walk
A chocolate bar will give you more energy than a weetbix
For us humans, us animals, 100% of our energy comes from our food.
Sitting in the sun might make you feel more awake, going for a run will get your heart pumping faster and giving a speech will make you sweat - but only Food will give you energy.
Have a look at the back of a chocolate bar and weetbix and it will tell you how much energy they have per 100 grams and per serve
Notice it is in Joules
Weetbix per 100g is 1480,000 Joules
Chocolate per 100g is 2320,000 Joules
Joules is the Unit for energy
K means 1000 - like if you buy a car for 8K that means 8000 dollars
So K means 1000, K= Kilo, so Kilo also means 1000
Kilojoules is simply 1000 Joules
Energy Concepts Summary Sheet
Energy Concepts Summary Sheet
Copy and paste and fill out this worksheet. It will help you strengthen your understanding of the key concepts related to energy.
Section 1: Summary Fill-in-the-Blanks
Use the words in the word bank below to complete the summary paragraphs. You might need to use some words more than once:
energy, created, potential, heat, perpetual motion, transformed, destroyed, kinetic, friction, Joules
Energy is the ability to do things. A very important rule in science is the law of conservation of _________________, which states that energy cannot be _________________ or _________________. It can only be _________________ from one form to another. The total amount of energy in the universe is always the same.
The two main categories of energy are stored energy, also called _________________ energy, and moving energy. An example of moving energy is _________________ energy. The unit we use to measure energy is _________________.
Whenever energy is converted from one form to another, some of it is always lost as _________________, usually because of _________________. For example, a skateboarder rolling on a ramp will eventually stop because their movement energy is turned into waste energy. This is the reason why _________________ machines, which could supposedly run forever, are impossible, as energy will always be lost to the environment due to friction as heat energy.
Section 2: Multiple Choice Questions
Cross out the incorrect (or just delete them)
1. What is the main idea of the Law of Conservation of Energy?
a) Energy is the same as power.
b) Energy can be made, but not destroyed.
c) The total amount of energy in the universe is constant.
d) Moving energy is more useful than stored energy.
2. A car is parked at the top of a hill. What type of energy does it have?
a) Kinetic energy
b) Gravitational potential energy
c) Heat energy
d) No energy
3. Why does a skateboarder on a half-pipe eventually stop? 🛹
a) They run out of energy.
b) Their energy is destroyed.
c) Friction converts their kinetic energy into heat energy.
d) Gravity stops working.
4. What is the standard unit for measuring energy?
a) Watts
b) Newtons
c) Volts
d) Joules
Section 3: Short Answer Questions
Write your answers in the space provided.
1. What is energy?
2. Describe the energy transformations that happen when a skateboarder rolls down a ramp.
3. Explain, using energy ideas, why a machine that can run forever without fuel (a perpetual motion machine) is impossible.
4. A Bouncing Ball: Imagine you drop a basketball. It hits the ground and bounces back up, but not as high as where you dropped it from. Describe all the energy changes that take place, starting from when you let it go to the moment it reaches the top of its first bounce. Make sure you explain why it doesn't bounce back to its original height.
Start: At its highest point, the ball has maximum ________________________________
Falling: As it falls, potential energy is transformed into ________________________________
Impact: When the ball hits the ground, it deforms (squashes). The kinetic energy is temporarily transformed into ________________________________
Bounce up: The elastic potential energy is transformed back into _____________________________, pushing the ball upwards.
Rising: As the ball moves up, kinetic energy is transformed back into ___________________________________________
Why it doesn't reach the same height:_______________________________________________________________________________
2. NCEA Level 1 Style Question:
A person bungee jumps from a platform high above a river. For a moment at the very bottom of the jump, the bungee cord is fully stretched and the person is not moving.
Explain, in detail the energy transformations that occur from the moment the person jumps until they are momentarily stationary at the bottom of the jump.
In your answer you should:
Name the main types of energy involved at the start, during the fall, and at the bottom.
Describe how energy is converted from one form to another.
Explain how the law of conservation of energy applies to the whole system, including where "waste" energy might go.
White Answers
White Answers
Worksheet Answer Key: I have made this WHITE. So, highlight it or select it with your mouse and you will see the answers. You can also copy and paste it then change the font to black
Section 1: Summary Fill-in-the-Blanks
The correct sequence of words for the fill-in-the-blanks section: energy, created, destroyed, transformed, potential, kinetic, Joules, heat, friction, perpetual motion
Section 2: Multiple Choice Questions
c) 2. b) 3.c) 4. d)
Section 3: Short Answer Questions - Answers
1. What is energy? Energy is the ability to do things or cause change.
2. Describe the energy transformations that happen when a skateboarder rolls down a ramp. At the top of the ramp, the skateboarder has stored gravitational potential energy. As they roll down, this potential energy is transformed into kinetic (movement) energy. Some energy is also transformed into heat due to friction.
3. Explain, using energy ideas, why a machine that can run forever without fuel (a perpetual motion machine) is impossible. It's impossible because in any real machine, some energy is always converted into non-useful forms like heat and sound due to friction. For the machine to keep going, this lost energy would need to be replaced, but since energy can't be created from nothing, the machine will eventually stop.
4. A Bouncing Ball:
Start: At its highest point, the ball has maximum gravitational potential energy.
Falling: As it falls, potential energy is transformed into kinetic energy.
Impact: When the ball hits the ground, it deforms (squashes). The kinetic energy is temporarily transformed into elastic potential energy.
Bounce up: The elastic potential energy is transformed back into kinetic energy, pushing the ball upwards.
Rising: As the ball moves up, kinetic energy is transformed back into gravitational potential energy.
Why it doesn't reach the same height: During the impact with the ground, some energy is converted into heat and sound. Air resistance also creates heat as the ball moves. Because the total useful energy of the ball is now less, it cannot bounce back to its original height.
NCEA Level 1 Style Question - Answer
At the start (on the platform): The jumper has maximum gravitational potential energy because of their height above the river. Their kinetic energy is zero because they are not moving.
During the fall: As the jumper falls, their gravitational potential energy is converted into kinetic energy, and they speed up. Once the bungee cord begins to stretch, both gravitational potential energy (as they are still falling) and kinetic energy are converted into elastic potential energy, which is stored in the stretching cord.
At the bottom: At the lowest point of the jump, the person is momentarily stationary, so their kinetic energy is zero. They are at their lowest point, so their gravitational potential energy is at its minimum. Almost all of the initial energy has been transformed into elastic potential energy stored in the fully stretched cord.
Conservation of Energy and Waste Energy: The law of conservation of energy states that the total energy is constant. The total energy at the start (gravitational potential) equals the total energy at the end (elastic potential + waste energy). However, energy is "lost" or wasted from the main system as heat due to air resistance as the person falls, and also as heat generated within the bungee cord as it stretches. Some energy is also converted to sound. Because of this waste energy, the elastic potential energy stored in the cord at the bottom will be less than the jumper's initial gravitational potential energy.
Past paper Powerpoint
Past paper Powerpoint
Questions and Answers
Questions and Answers
This is a google slides (google powerpoint). Just click the arrows to see the questions, usually the answers are on the next slide. These are from NCEA past papers
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