What is power and what is energy

Strength and energy

(Course level > mechanics)

(Classic mechanics > Conservation of energy)

Energy transfer with forces

If a force acts in parallel along a path, energy is transferred. If the force is perpendicular to the path, this is not the case, only the direction is changed (circular movement). If it is inclined, only the parallel component is effective. If a force works without movement, no energy is transferred. (Holding heavy objects and human muscles ?!)

The male exerts a force F in the direction of the path s on the cart. The energy [math] E = F \, s [/ math] is transferred from the male to the car. You can see that from the fact that the car is getting faster. The car receives kinetic energy (kinetic energy).

In this case, the male exerts a force opposite to the direction of movement of the cart. It slips across the floor. During this process the car loses its kinetic energy [math] E = F \, s [/ math] and this is converted into thermal energy (reloaded to entropy) through the friction between the male and the ground.

The male pulls the sledge at a constant speed. Because of the friction, a force is required!

The force in the direction of the movement thus transfers the energy into the movement of the slide and the equally large frictional force ensures that the energy [math] E = F \, s [/ math] immediately returns from the movement to the warmth of the runners and the Snow is transferred.

Here the male exerts a force (F) on the kite. However, since this is directed at an angle to the direction of movement of the kite, only the parallel force [math] F_ {||} [/ math] effectively acts on the kite. So only energy in the amount of [math] E = F_ {||} \, s [/ math] is transferred.

This example is similar to the example with the kite, because here too the male exerts an oblique force. So we have to look at the force [math] F_ {||} [/ math], which is parallel to the direction of movement of the slide, in order to find out how much energy is transferred.

A classic example of a circular motion: the earth rotates around the sun, the centripetal force always being perpendicular to the direction of motion. So no energy is transferred, only the direction of movement is changed.

Amounts of energy in the force-displacement diagram

  • With a constant force in the direction of the path, the increase in energy [math] \ Delta E = F \ cdot s [/ math] corresponds to the rectangular area under the graph.

  • If the force acts against the direction of movement, the area is rated as negative. The amount of energy drops by [math] \ Delta E [/ math].

  • If you stretch a spring, the force increases proportionally to the path. The amount of energy put into it corresponds to a triangular area.

  • Even with a variable force, the amount of energy transferred is calculated as the area under the graph.

  • With this spring oscillation, the pendulum receives energy at the beginning, ...

  • ... to hand them over again after passing through the rest position.

Formulas for forms of energy

Positional energy, kinetic energy, tension energy

E = mgh E = 1 / 2mv ^ 2 E = 1 / 2Ds ^ 2

Energy balances

  • As everywhere, the conservation of energy applies
  • Energy balances roller coaster, pendulum, etc.