Performance Indicator 5.2
Observe, describe and compare effects of forces (gravity, electric current, and magnetism) on the motion of objects.
1. Every object exerts a gravitational force on every other object. The force depends upon two factors:
2. Electric currents and magnets can exert a force on each other.
Electric current is the flow of electrons. Stationary electricity is called Static Electricity. Static electricity is the build up of negatives charges. Then the release of these charges is an electric discharge. The law of electric charge states that objects with the same charge will repel each other and objects with different, or unlike charges will attract each other.
Similar is true for magnets. Magnets have two poles, a north and a south. Like poles repel and opposite poles attract.
Magnets are made up of little domains (little blocks of + and - or north and south) that all point in the same direction. Leaving all the norths pointing one way and the souths pointing the other. If a magnet were to be cut in hafh, the result would be two magnets each with a north and south.
3. Friction is the force that opposes motion.
What happens to a car that is just coasting? It will eventually slow down due to the effects of gravity and friction between the road and the wheels of the car. Friction is best felt when you rub your hands together. The result is heat. Heat is a biproduct of friction.
Friction os the reason why you do not fall or slip when you are walking. If the surtface is slippery, like ice, you have reduced friction and my slip and fall. When we increase friction we will use something rough or sticky.
There are times when we want to decrease friction. We used oil in a cars engine to decrease friction. We reduce friction on a pool slide by adding water to the slide. Some common ways to reduce friction by using lubricants or waxing surfaces.
4. A machine can be made more efficient by reducing friction.
5. Simple Machines will change the size or direction of a force in one motion. Compound Machines a system of two or more simple machines (the game mouse trap is a great example).The following is a list of what machines do:
Machines have what is called mechanical energy, the energy of moving things. Some examples of mechanical energy are: wind, moving rocks, and waterfalls. The energy output compared to the energy input is called efficiency.
6. Simple Machine include the following: inclined plane, lever, pulley, wheel and axle, wedge, gears. A comination of two or more simple machines make a compound or complex machine. (ex. scissors, can opener, bicycle.)
