Concept Of Physics

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Concept of Physics

Energy, strength, power and efficiency

Before explaining the concept work as described or understood physics, we will review or a reminder of that wonder that moves the world and is called Energy.

Energy

It is defined as energy that capacity of a body (mass) to work after being subjected to a force , ie, the work cannot be done without power . This capacity (energy) can be given by the position of a body or its speed, which is why we can distinguish two types of energy:

Potential energy

It is the energy possessed by a body (mass) when in stationary position.

For example, a lamp hanging from the ceiling of the dining room you can, if it falls, breaking the table. While hanging, has a latent ability to produce work. It has potential energy, and therefore is called potential energy.

Generally, this means that a body of mass m at a height h , having a potential energy calculable by the formula

The formula should be read as: potential energy (Ep) is the product of mass (m) by the gravity constant (g = 10 m/s2) and the height (h).

The unit of measurement for energy is the same work, the Joule.

Referred to power a Joule is the amount of energy required to raise a kilogram mass at a height of 10 cm from the surface of the Earth.

Another unit of energy is calories. A Joule equals 0.24 calories.

If we move from Joules to calories just multiply the amount by 0.24 and in the opposite case the divide by 0.24 to obtain Joules.

Practice Exercise:

A 2 kg book resting on a table 80 cm, measured from the floor. Calculate the potential energy that has the book in relation

a) with the floor

b) the seat of a chair, located 40 cm from the ground

Development:

First, let us note that we have the data:

m = 2 Kg (mass of the book)

h = 80 cm = 0.8 m (height at which the book is and from which "may fall")

g = 10 m / s 2 (gravitational constant) (actually 9.8)

Regarding the chair:

h = 40 cm = 0.4 m (the difference between the height of the table and that of the chair)

We know the formula for calculating potential energy will (Ep):

Then, we solve:

Case a)

Answer: On the floor (ground), the book has a potential energy (Ep) of 16 Joules.

Case b)

Answer: As for the chair, the book has a potential energy (Ep) of 8 Joules.

Kinetic energy

It is the same potential energy that has a body but becomes kinetic when the body is set in motion (moves at speed).

The wind moves the blades that rotate and produce new energy.

For example, to drive a nail have to hit it with a hammer, but the hammer to do so should have some speed to hit the nail hard and perform a job , this is the kinetic energy  (Moghaddam et.al, 2010).

Clearly, we should note that here we have incorporated the concept of speed. Then, in general, a body of mass m moving with velocity v, has a kinetic energy given by the formula.

This formula reads as kinetic energy (KE) is equal to one half (1/2 = 0.5) of the mass (m) times the square body speed (v 2 ).

Practice Exercise:

A planter 0.5 kg mass falls from a window (where it was at rest) which is at a ...