The Currency of the Universe
Energy is what allows us to run, machines to work, and lightbulbs to glow. It is the ability to do work, cause change, or make things happen.
The Universal Currency
Think of energy like money; you can spend it in different ways, but the total amount remains the same.
The Unit of Measure
We measure energy in Joules (J).
Fun fact: One Joule is roughly the energy needed to lift a small apple one meter into the air!
Transformative Nature
Energy never simply disappears. It just puts on a new disguise, transforming from one type into another.
Energy makes everything in our universe possible.
Kinetic Energy (KE)
The energy of motion.
Kinetic Energy is the energy an object possesses due to its motion. If it is moving, it has kinetic energy.
The amount of kinetic energy depends on two factors: mass ($m$) and speed/velocity ($v$).
KE = ½ m v²
- m = mass in kilograms (kg)
- v = velocity in meters per second (m/s)
- KE = Kinetic Energy in Joules (J)
Because speed is squared in the formula, doubling your speed actually quadruples your kinetic energy!
KE Calculator
400 J
Potential Energy (PE)
Stored power waiting to be released.
Gravitational Potential
Energy stored due to an object's height above the ground.
The higher you lift an object, and the heavier the object is, the more gravitational potential energy (GPE) it stores. Think of a roller coaster paused at the very top of a massive drop.
PE = mgh
m = mass, g = gravity (9.8 m/s²), h = height
Quick Calc
Elastic Potential
Energy stored when an object is stretched, compressed, or bent.
A pulled rubber band, a drawn archery bow, or a compressed spring all contain high amounts of elastic potential energy just waiting to be released.
The Mighty Flea
A common flea can jump over 100 times its own height! It achieves this by storing elastic potential energy in a special pad made of a protein called resilin in its legs, releasing it like a tiny, powerful spring.
The Ultimate Rule
it can only be transferred or changed from one form to another."
— The Law of Conservation of Energy
Falling Object Simulator
Mechanical Energy (ME) = ConstantDrag slider to drop the object
As the object falls, it loses height (losing PE) but gains speed (gaining KE). The total mechanical energy in a perfect system remains exactly the same!
Want to explore more? Try the University of Colorado's interactive Energy Skate Park!
Open Energy Skate Park SimulatorEnergy in the Real World
Reflecting on the Impacts of Science.
Pumped-Storage Hydroelectricity
A local government is considering building a "pumped-storage hydroelectric dam" in a nearby mountain valley to solve their town's power shortage.
- At night, when power is cheap, they use electricity to pump water up a mountain into a reservoir (storing Gravitational Potential Energy).
- During the day, when everyone needs power, they let the water fall back down through turbines (turning to Kinetic, then Electrical Energy) to generate electricity.
Functional Energy Literacy
What is a Watt?
We don't just use Joules in real life. When you look at an appliance, you see its power consumption in Watts (W) or Kilowatt-hours (kWh).
Reading the Label
Energy rating labels use color codes (green to red) and letter grades (A to G) to tell consumers how efficiently a fridge or TV uses electrical energy. Understanding these helps families save money and protect our planet!
Knowledge Check & Tasks
Test your skills based on Criterion A (Calculations) & Criterion D (Impacts).
Criterion A: Knowing and Understanding
Level 1-2: Emerging (Recall and Simple Application)
Q1: In your own words, state the difference between kinetic energy and gravitational potential energy.
Q2: A 5 kg bowling ball is resting on a shelf that is 2 meters high. Calculate the gravitational potential energy of the bowling ball.
Q3: A 50 kg student is running at a velocity of 4 m/s. Calculate the student's kinetic energy.
Level 3-4: Developing (Applying Knowledge)
Q1: An archer pulls back a bowstring and releases an arrow. Outline the specific energy transformations taking place.
Q2: A cheetah has a kinetic energy of 2800 J while sprinting at a velocity of 20 m/s. Calculate the mass of the cheetah.
Q3: A drone has 1470 J of gravitational potential energy while hovering in the air. If the drone has a mass of 3 kg, calculate how high it is flying.
Level 5-6: Proficient (Complex Situations)
Q1: A 60 kg skateboarder is standing at the top of a frictionless halfpipe that is 4 meters deep.
- A) Calculate their maximum potential energy at the top.
- B) Using the Law of Conservation of Energy, determine their kinetic energy the exact moment they reach the bottom of the halfpipe.
- C) Calculate the skateboarder's velocity at the bottom of the halfpipe.
Level 7-8: Mastery (Evaluating Unfamiliar Situations)
Q1: A 1000 kg roller coaster car drops from a 50-meter-tall hill. It travels through the track and comes to a stop at the top of a second hill, which is only 40 meters tall.
- A) Calculate the mechanical energy the car lost between the first and second hill.
- B) Explain, using scientific reasoning, where this "lost" energy went and why the second hill can never be taller than the first.
Criterion D: Reflecting on the Impacts of Science (Pumped Hydro)
Refer back to the "Pumped Hydro" tab for the context scenario to answer these questions.
Criterion D Task Discussion Points
Scientific Solution
How it works: Excess electrical energy at night does work to pump water uphill, converting electrical energy into Gravitational Potential Energy. During peak daytime demand, water flows down, converting PE to Kinetic Energy, spinning turbines to generate Electrical Energy.
Energy Loss: While Mechanical Energy is ideally conserved, real-world pumping and turbine spinning involves friction. Some energy is lost to the environment as thermal energy, meaning you get less electricity out during the day than you used to pump the water up at night.
Implications & Trade-offs
- Economic (Positive): Provides reliable power during peak hours preventing blackouts. Creates local jobs for construction and maintenance. Can sell expensive daytime power while using cheap nighttime power.
- Environmental (Negative): Flooding a mountain valley destroys local terrestrial habitats, displaces wildlife, and alters downstream water flow and aquatic ecosystems.
- Evaluation: Is the destruction worth it? (Students must justify their stance based on the need for clean, reliable energy storage vs local ecological damage).
"Energy is the ultimate currency of the universe."