1. Friction, Gravity, and Elastic Forces Understanding how force cause the interaction in the natural world.

2. Friction Friction is a force that works frequently in the opposite direction as the object is moving.Friction is a force that works frequently in the opposite direction as the object is moving. Friction is caused when two objects rub together and create heat.Friction is caused when two objects rub together and create heat. The source of friction is the combination of mass, surface area, and gravity.The source of friction is the combination of mass, surface area, and gravity.

3. The Four Types of Friction There are four types of friction. Static friction- friction from an object which is not moving. Sliding friction- friction that occurs when two solid objects slide over each other. Rolling friction- this occurs when an object rolls over a surface. Fluid friction- occurs when a solid object moves through a liquid.

4. Gravity Gravity is a force which pulls objects towards each other. Gravity on Earth is the force which pulls objects straight down and into the surface of the Earth toward the core. The law of universal gravitation states that forces of gravity act between all objects in the universe. The two factors that effect gravity are mass and distance. The closer two objects are the more force gravity has between the two objects. The more mass an object has the greater the amount of force an object can generate. In summary an increase in mass or a decrease in distance between two objects results in an increase in the force of gravity.

5. Gravity and weight The term weight refers to the force of gravity on an object. The weight of an object can be altered or affected by location even through the force of gravity on the Earth is a constant. Although the mass of an object remains the same, because the force of gravity is different between the Earth and the Moon this is the reason why astronauts weigh about 1/7 th on the moon what they weigh on Earth. Weight is defined by mass x acceleration due to gravity. Weight = Mass x Acceleration due to gravity. Wt on moon 270 N Wt on Earth 1617 N Mass on Moon 165 kg Mass on Earth 165 kg

6. Gravity and Motion Free fall is when the force of gravity is pulling an object straight down.Free fall is when the force of gravity is pulling an object straight down. An object in free fall accelerates at a rate of 9.8 m/s during free fall.An object in free fall accelerates at a rate of 9.8 m/s during free fall. Air resistance is a form of fluid friction which occurs when a object in flight or falling down is effected by air molecules.Air resistance is a form of fluid friction which occurs when a object in flight or falling down is effected by air molecules. Projectiles are objects which are thrown through the air and are effected by both air resistance and gravity.Projectiles are objects which are thrown through the air and are effected by both air resistance and gravity.

7. Elastic Forces When objects are thrown horizontally they travel in a projectile motion.When objects are thrown horizontally they travel in a projectile motion. Matter is considered elastic if it returns to its original shape after it is squeezed or stretched.Matter is considered elastic if it returns to its original shape after it is squeezed or stretched. –Compression is an elastic force that squeezes or pushes matter together. –Tension is an elastic force that stretches or pulls matter.