If you slide a bool across a table, the surface of the book against the surface of the table. The resulting force is friction. This force acts in a direction opposite to the motion of the book and eventually stops the book. Both the types of surfaces involved and how hard the surfaces are pushed together affect the friction between two surfaces. Smoother surfaces produces less friction than rougher surfaces. Friction increases as surfaces push harder against each other. Frictions acts in a directions opposite to the directions of the objects motion. Without friction or some other force acting in the opposite direction, a moving object will not stop until strikes another.
There are 4 types of friction: rolling, sliding, fluid, and static friction. Rolling friction occurs between 2 smooth surfaces. An example of this is rolling on a skateboard. Sliding Friction is similar to rolling friction but it is what makes moving objects slow down and stop. Fluid friction such as water and air, flow easily. Fluid friction occurs when a solid object moves through a fluid. Fluid friction from your contact with water acts on your body when you swim. When an object moves the fluid friction acting on it is often reffered to as air resistance. Finally, static friction acts on objects when they are resting on a surface.
Gravity is a force that pulls objects toward each other. Gravity is experienced on Earth through throwing an object in the air and then the object being attracted to the earths core. Isaac Newton concluded that a force called gravity acts to pull objects straight down toward the center of Earth. Newton realized that gravity acts everywhere in the universe, not just on Earth. This is called the law of universal gravitation. This law state that force of gravity acts between all objects in the universe that have mass. So, any two objects in the universe are attracted to each other.
The factors that control the strength of the gravitational force between the two objects are the mass of each object and the distance between them. The more mass an object has the greater the gravitational force between it and other objects. Earth’s gravitational force on nearby objects is strong because the mass of the Earth is so large. Gravitational force also depends on the distance between the objects’ center. As distance increases, gravitational force decreases. Mass is a measure of the amount of matter in an object. Since weight is a measure of, the SI unit of weight is a newton (N). If you know the mass of an object in kilograms, you can calculate its weight on Earth using Newton’s second law. Net force= Mass x Acceleration. If you could stand on the surface of Jupiter which has a mass around 300 times the mass of Earth your mass would remain the same because you have the same amount of matter in your body as when you were on Earth, but your weight would increase. This is because the gravitational force exerted on you is greater on Jupiter than Earth.
There are several different types of potential energy, based on different types of forces. The type of potential that we associate with gravity is called gravitational potential energy. On Earth, gravitational potential energy (GPE) is based on an objects position. The higher up the object the greater its GPE. GPE= Mass x Acceleration due to gravity.
When a skydiver jumps from a helicopter, a net force acts on his body as he falls. Thsi net force is a combonation of gravity and frction. Gravity pulls him down to the ground and fluid friction acts on him in the opposire direction as he falls through the air. However, these forces are unbalanced, the forces of gravity is stronger than the air resistance, so he accelerates downwards.
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