# How does kinetic energy increase speed

## The law of conservation of energy

**Table of Contents **

• What are forms of energy?

• What does the law of conservation of energy say?

• Examples

• The most important formulas

### Forms of energy

Energy occurs in nature in many different forms. These include:

### Statement of the law of conservation of energy

The EES states that the total energy of a closed system is constant. A closed system describes, for example, a box that does not let any energy in or out. This clearly means that all possible forms of energy can be converted into another form, but that the sum of all forms of energy is constant. Energy can neither be destroyed nor generated from nothing. Energy can only be converted from one form to one or more others at a time.

### Illustrative examples

With the help of the EES, many physical tasks and problems can be solved. Here are some examples:

- When a moving car brakes, its kinetic energy is reduced.

However, the braking process heats up the brakes, their thermal energy

increases. The thermal energy of the brakes increases by exactly the amount

by which the kinetic energy of the car decreases. The sum of kinetic

Energy and thermal energy is constant. - A ball is thrown straight up into the air. At first he owns one

high speed. However, this becomes smaller until the ball is momentarily

comes to rest and then falls back down. As the ball rises

its potential energy increases in the earth's gravitational field. These

Energy has to be subtracted from the kinetic energy of the ball, the ball

becomes slower as a result. Again: The sum of the kinetic and the potential

Energies of the ball is constant. - A motor is z. B. powered by gasoline. By burning

Gasoline releases chemical energy, some of which translates into the kinetic energy of the pistons

is used in the engine. However, a large part of the energy is lost as heat

and cannot be used. If one calculates the released thermal energy

as well as the kinetic energy of the pistons together, the sum is just that

chemical energy of the gasoline that was released. The products of combustion

of gasoline have a lower chemical energy by this amount. - A spring is stretched. This requires a certain amount of energy, which is called

elastic energy is stored in the spring. Now you put a mass on

and lets go of the spring, the mass is thrown away and the spring turns

back to sleep. The elastic energy is converted into kinetic energy

converted to the mass.

Bills to these **Examples** can be found below.

### The most important formulas

In the following, m is the mass, v is the speed, g is the acceleration due to gravity, k is the

Spring constant, T the temperature and C the specific heat capacity per mass.

The kinetic energy of a mass m moving with velocity v is

E. _{kin} = 12 mv ^{2} : 1

The potential energy of a mass m at height h is relative to the reference height h0

E. _{pot} = mg (h - h _{0} ) : 2

The elastic energy stored in a deformed spring constant is

E. _{el} = 12 kx ^{2} : 3

where x is the deformation of the spring in meters.

In a mass m with a specific heat capacity C, with a change in temperature

The following heat energy is absorbed or released by ΔT:

E ~ th = mC ΔT: 4

C is a material size and can be looked up in tables.

These formulas can be used to solve most of the school tasks that require the EES.

### Mathematical application

The above examples are calculated with typical numerical values and the corresponding formulas.

_{1}= 30 m / s. It brakes

v

_{2}= 10 m / s. The di erence of the kinetic energies at the beginning and at the end

is E = 12M (v21-v22) = 600 kJ. This energy is converted into the thermal energy

Brakes converted. Assume that all of the brakes have a mass

of m = 10 kg with a specific heat capacity of C = 400 J / kgK

typical of steel, the brakes would turn around

ΔT = EmC = 150 K

heat, e.g. from 20 to 170 ° C.

v = 10 m / s upwards. He is thus able to use his potential energy

E = 12 mv

^{2}= 5Y

to increase. At the point of greatest height, the ball has no kinetic energy

more. The ball does not move at this moment. The energy E is now there

completely in the height change of the ball that

Δh = Emg = 5m

if g ≈ 10 m / s

^{2}is used.

amount to 30%. That is, 30% of chemical energy is turned into kinetic energy

the piston is converted, the rest is lost as waste heat and thermal energy

cannot be used. One liter of gasoline contains about 36 MJ of chemical substances

look up usable energy in tables. Since only 30% can be used by us,

only E = 10.8 MJ of energy remain. The remaining 25.2 MJ are directly transferred to

Heat converted and are not used for the movement of the pistons.

With the energy E, for example, a mass m = 1000 kg can be achieved

Δh = Emg = 1080m

raise. A small car can therefore be more than a kilometer in the air

be lifted.

E = 12 kx

^{2}= 0.25J.

This is completely converted into kinetic energy with a mass of m = 20 g. The

Mass then moves at a speed of

v = 2 Em = 10 cm / s.

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