# What exactly is the total energy ?

• Olijet
In summary, the conversation discusses the calculation of total energy in a system where a 20kg mass is suspended at a height of 5 meters above the ground on the moon. The equations used are kinetic and potential energies, and the total energy is equal to the sum of these two. The concept of energy conservation is also mentioned, and it means that the total energy remains constant in an isolated system. The numerical value of the constant can vary depending on the initial energy and any changes in the system.
Olijet

## Homework Statement

A mass of 20kg is suspended at a high of 5 meters above the ground. It is on the moon (then acceleration = 1.635 m/ss). It falls, and we want to know the total energy halfway, at 2.5 meters above the ground.

## Homework Equations

I suppose the equations I need to use are kinetic and potential energies :
Ek = 1/2.m.v2
Ep = m.g.h

## The Attempt at a Solution

Once I have the values for Ek and Ep, can I proceed like this : Etotal = Ek + Ep ?
I have seen on many physics books that without friction, the Et is constant. But what means that constant ? Is there any numeric values ? What do I have to answer at the question : what is the Etotal ?

Thank you very much for your help,

Olijet

The constant itself could take on any numerical value depending on what units you use. Suppose, for example that you calculate the energy as say 20J in the initial configuration. The total energy will remain 20J no matter how the configuration of the system changes. So, if the gravitational potential energy is reduced by half (10J) then that 10J must have gone into some other form of energy (say, kinetic energy).

So if the question asks for the total energy and there are no dissipative forces (like friction) the total energy will be equal to whatever the initial energy is. If the question asks for the kinetic energy or speed, you can easily calculate this based on the conservation of energy principle I described above.

Hi brainpushups,

Ok, it is becoming more clearer now. So it means this constant can be a different numerical value depending on the isolated system...

Thank you for your help !
Olijet

## What exactly is the total energy?

Total energy refers to the sum of all forms of energy present in a system, including kinetic energy, potential energy, thermal energy, and any other types of energy. It is a measure of the ability of a system to do work or cause change.

## How is total energy calculated?

Total energy is calculated by adding up the individual energies within a system. For example, for a moving object, the total energy is the sum of its kinetic energy (due to its motion) and its potential energy (due to its position in a gravitational field). In more complex systems, such as chemical reactions, the total energy is calculated by considering the energy of each molecule involved.

## What is the difference between total energy and internal energy?

Total energy refers to the energy of a system as a whole, including both its internal and external forms of energy. Internal energy, on the other hand, refers specifically to the energy stored within the particles of a system, such as the kinetic and potential energies of atoms and molecules.

## How is total energy conserved?

According to the principle of conservation of energy, the total energy of a closed system remains constant over time. This means that energy cannot be created or destroyed, only transferred or converted from one form to another. In other words, the total energy of a system before and after a process or event will remain the same.

## Why is understanding total energy important in science?

Total energy is a fundamental concept in science and is used to understand and describe a wide range of phenomena, from the motion of objects to chemical reactions to the behavior of the universe. By understanding total energy, scientists can make predictions and explain the behavior of systems, and develop new technologies and solutions.

Replies
10
Views
3K
Replies
5
Views
2K
Replies
4
Views
1K
Replies
19
Views
2K
Replies
1
Views
3K
Replies
1
Views
2K
Replies
14
Views
2K
Replies
4
Views
2K
Replies
10
Views
3K
Replies
38
Views
4K