# Where are the laws of physics kept

This program from Telekolleg-Physik deals with the connection between acceleration, accelerating force and the "inert" mass of an object. This second Newton's law occupies a prominent position in mechanics. The program is divided into the following sections:

When an aircraft takes off, a passenger clearly experiences the physical parameters that play a role in this program: On the one hand, the accelerating force that presses him or her into the seat; furthermore the rolling noises, which convey the feeling for the great acceleration, and finally, when the take-off speed is reached, the reassurance that it has once again been possible to get the enormous aircraft mass to fly.

The glider is pulled up with a rope by a winch.

In the case of a glider, the accelerating force is applied from outside via a pull rope. At the end of the runway there is a vehicle with a strong motor winch. This accelerates the glider and pulls it to a high take-off altitude.

### Acceleration due to gravity

Also the Weight force causes an acceleration that Acceleration due to gravity
G = 9.81 m / s2.

"Weightlessness" in space

The weight force is not perceived in space, here all objects remain free-floating at rest or they move at a constant speed as long as no accelerating force acts on them.

### Demonstration of the principle of inertia

To demonstrate the principle of inertia, a straight stretch of a toy train was built into a tram:

When the S-Bahn brakes, the toy train accelerates

As soon as the tram brakes, from the perspective of the passengers, the carriages of the fairway start moving forward because they stand on their toy rails without any particular friction.

The braking process leads to a speed difference.

An observation from an outside position reveals this apparent acceleration as a movement with constant speed.

A ball lies on the rolling cart.

A similar phenomenon occurs when cornering: a ball lies unattached on the loading area of ​​a wagon behind a toy locomotive.

The ball maintains its direction of movement in the curve.

As soon as the train turns into a curve, the ball rolls off the car. But here, too, there is no external force! On the contrary, because there is no force acting on it, the ball retains its original direction of movement.

The napkin trick - pull as jerkily as possible

A trick to the phenomenon of inertia: With one jerk a sheet of paper is pulled away from under a container without spilling anything.

This school experiment was the model for a bet in a TV show: the tablecloth of a very long wedding table was pulled away in a car so quickly that (almost) all the dishes remained intact.

Structure of a dynamometer: spring, pointer and scale

A dynamometer consists of a coil spring to which a pointer is attached and a scale calibrated in Newtons.

The elongation of the spring is a direct measure of the force acting on the unit Newton or a multiple.

Holding force of 140 N when braking

For example, it can be used to measure forces that occur in vehicles when accelerating or braking. In a bus, standing passengers have to hold on with a certain amount of force so that they do not fall forward when the bus stops. Forces can also be felt when moving off quickly.

A wagon of the toy train is provided with a propeller drive, which provides a constant accelerating force.

In order to determine the relationship between mass and acceleration, different pieces of mass are placed and then the acceleration is measured in each case.

Acceleration measurements with constant force and different mass

If the mass is doubled, the acceleration is halved - a is indirectly proportional to m. In a second series of tests, the mass is kept constant and the acceleration is measured for various forces:

With double the force, the acceleration doubles - a is proportional to F.. Overall, the force law results: F. = m · a.

Items weighing 1 kg each: Styrofoam, wood, aluminum, lead.

After international definition of units (SI = S.ystème I.nternational d’Unités) is that kilogram a Basic size, as well as meter and second. The units for acceleration and force are derived from this.

Standard kilogram in Paris with vacuum bell and dust cover

Objects with a mass of 1 kg have very different sizes depending on the material.

In an institute near Paris, the so-called Standard kilograms kept.

Weight G of 9.81 N on a mass of 1 kg

Weight acts on every mass G; this causes the acceleration due to gravity in free fall G. If the mass is at rest, then the holding force must be the same G be.

On the moon, the weight is only one sixth as great as on earth, so the "moon acceleration" is only one sixth of the acceleration due to gravity.
Astronauts on the moon have a weight Gmoon of only 1/6 of Gearth.

Crash test at 53 km / h against a rigid wall

In a crash test, enormous braking delays occur which, according to the law of force, cause enormous forces on the occupants. A slow motion study allows a calculation:

Calculation of the acceleration and the force on a crash test dummy

A force of 17 kN acts on a driver who weighs 80 kg! This corresponds to a weight on a mass of 1.7 tons and leads to very serious injuries. That is why it was mandatory for drivers to wear seat belts.