Restoring force
The restoring force F r is a force that acts on a mass that has moved out of its rest position . The restoring force acts back in the direction of the rest position of this mass, it wants to "reset" the mass to its rest position.
The restoring force occurs z. B. for deflections of elastic springs on:
- When used in measuring devices , it is proportional to the value of the measured variable , e.g. B. that of the electrical current in a moving coil measuring mechanism .
- When a spring-mass system oscillates, it acts repeatedly in alternating directions, but always to the rest position of the mass, e.g. B. when springing a vehicle .
A restoring force can also be effective on a body when it can move freely into a lower position with less potential energy , e.g. As a drop serene stone.
Restoring force in the event of vibrations
With pendulum threads or columns of water in U-tubes, there is repeated reversal of movement ( vibration stimulated by gravity ).
In the absence or neglect of other forces, Newton's law applies : When the deflection increases from the rest position, the restoring force leads to a reduction in the speed (negative acceleration ) of the oscillating mass and when the deflection decreases, it increases the speed (positive acceleration) .
The restoring force reaches its maximum value at the reversal points of the oscillation. At the zero crossings, i.e. H. when passing the rest position, the restoring force is zero.
If the restoring force is proportional to the deflection, one speaks of a harmonic oscillation .
example
The following applies approximately to the spring pendulum :
With
- D = spring constant
- s = deflection.
The minus sign means that the restoring force and the deflection of the pendulum are directed in opposite directions; if you are only interested in the amounts of the quantities involved, the minus sign can be omitted.