If you're seeing this message, it means we're having trouble loading external resources on our website.

If you're behind a web filter, please make sure that the domains *.kastatic.org and *.kasandbox.org are unblocked.

Main content

### Course: Middle school physics - NGSS>Unit 3

Lesson 3: Changes in energy

# Changes in energy

Review your understanding of changes in energy in this free article aligned to NGSS standards.

## Key points:

• Energy can’t be created or destroyed. If one object loses energy, another object has to gain that energy.
• Energy can be converted into different forms. For instance, a hairdryer takes electrical energy and converts it into thermal energy.
• When an object’s motion changes, so does its energy. If a bicycle slows down, it loses kinetic energy. That kinetic energy will be converted into another form, such as thermal energy, or transferred to another object.
• When a force acts on an object the energy of that object changes. For instance, when you hit the brakes on a bike, you’re applying a force to the wheels. That force converts some of the kinetic energy into heat.

## Want to join the conversation?

• it says that if one object loses energy then another object gains that energy, so if you're sick and you lose some energy where does it go?
(15 votes)
• When energy is lost, it is usually converted into heat1. For example, when waste and dead matter are broken down by decomposers, the nutrients are recycled into the soil to be taken up again by plants, but most of the energy is changed to heat during this process1. However, the energy is still present in the system as kinetic energy. To bring the system to rest, the kinetic energy of the system must be transferred to some other part of the system1.
(28 votes)
• Does velocity matter in transfer of energy
(12 votes)
• Yep! There is a formula for Kinetic energy that says KE = half of your mass times your velocity squared (1/2 m v^2). So if two rocks both transfer all their energy somewhere, and both have the same mass, but one of them has a much greater velocity, then the one with the greater velocity will transfer more energy! This makes sense if you think about how much of a splash you can make in a pond by throwing a rock much harder (more velocity) or much softer, for example.
(10 votes)
• i like how math help the earth but not me.
(17 votes)
• 2+2 is the equation to solve earths problems but not my problems im going to cry lol
(1 vote)
• If energy can’t be created how does it form
(12 votes)
• It can't be formed, according to the Law of Conservation of Energy.
(4 votes)
• If energy didn't exist, how would it change our lives today?
(9 votes)
• We would probably not move and be nothing.
(10 votes)
• This comment section is way better, back in the biology section the comments section literally just turned into a censored, cuss-free version of reddit
(11 votes)
• If water freezes and becomes ice, will it have the same weight as before? (i know that its different volume and mass, but how about weight) ? pls explain
(6 votes)
• #Meow🤣, anyways yes, the water would have the same mass as the ice because no matter the form of anything it will always be the same mass or have the same mass.

Sorry I'm 17 Days late but Hope this helps! :)
(5 votes)
• if you have two of the same mass of a ball and one faster why would that be ^-^
(7 votes)
• because though they have the same mass they have different speed
(3 votes)
• If energy cannot be created, why does it exist in the first place?
(6 votes)
• Answer:

When the universe was created, the protons, neutrons, and electrons needed for atoms and molecules already existed. Hydrogen is made up of 2 protons and 2 electrons. When it fuses, it creates heat energy and light energy. That energy came from the atom, and that energy came from the protons and electrons that already existed before the universe was born. When it fuses, it also creates a new element: Helium. This creates a buildup of new physical elements, and slowly that universe will turn from empty proton space into a large amount of atoms that can create stars, galaxies, and nebulas, which all will create new things. Energy is basically an infinite family tree with no beginnings.
(4 votes)
• nice how do i become potential energy
(4 votes)
• Find Master Wu. He'll help you reach your true potential.
(4 votes)