Musular Force

Muscles make it possible for animals to move. They are attached to the bones. Most muscles are controlled by the brain. Messages from the brain travel through nerves and tell the muscles when to act. Unused muscles go soft. Exercise and a proper diet that includes lean meat, milk, and cheese help to build strong muscles. 

The force Of Friction 

When two surfaces are rubbed against one another, one tends to stick to the other. Friction is the force that causes this. No surface is perfectly smooth. Even the smoothest looking surface, when examined with a microscope, will be seen to have bumps and hollows. These bumps and hollows resist one another when two surfaces are rubbed together. The force of resistance is called friction. Friction can be useful. Rub the palms of your hands together, pressing hard. Do this quickly several times. Your hands begin to feel warm. This shows that friction produces heat.

What Can Forces Do?

Forces can make things move. They can also act on stationary objects without causing motion. Sometimes we use a force on an object that is already moving, to stop it. A train uses a braking force as it approaches a station. Similarly, when astronauts were about to land on the moon, rockets were used to slow down their craft, so it could make a soft landing. Forces can also change the direction of motion. This happens in baseball when a batter hits the ball. The ball is first slowed down, then stopped for an instant, then shot off in a different direction. 

 The Force Of Gravity

This is the force that pulls objects down to the ground. when we say a rock is heavy, we mean that the force of gravity pulling down on it is a strong force. To lift the rock off the ground, you must use a force that is slightly greater than the pull of gravity. Once the rock is moving upwards, the lifting force becomes equal to the gravity force. The force of the Earth's gravity is what holds the moon in its nearly circular path around the Earth and prevents it from flying off into outer space. Similarly, it is the force of the sun's gravity that keeps the Earth and the other planets in their orbits.

Culture Media

A culture medium must contain a balanced mixture of the required nutrients, at concentrations sufficient to allow a good growth rate. If a nutrient is in excess, it can inhibit growth or even be toxic. Often one nutrient is present in limiting quantities, to allow adequate growth while preventing the microorganisms from multiplying at their maximum rate. By moderately slowing down the growth rate, the microorganisms are kept healthy. Usually a mineral base is made, containing all the possible nutrients in inorganic form. To this can be added a carbon source, energy source, nitrogen source and growth factors, to suit the organism being cultured. A medium composed entirely of chemically defined nutrients is called a synthetic medium. A medium which contains some ingredients of unknown chemical composition, such as malt extract, is called a complex medium.