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• Friction
• Friction is a force that two surface exert on each other when they rub against each other  The causes of Friction  The strength of the force of friction depends on the types of surfaces involved and on how hard the surface push
• Types of Friction
• Static friction happens when friction acts on an object that is moving. Sliding friction happens when two solid surfaces slide over each other. Rolling friction is when a solid object moves through a fluid. Fluid friction occurs when a solid object moves through a fluid.
• Gravity
• ﻿Gravity is the force that pulls objects towards each other. The force of gravity between objects increases with greater mass and decreases with greater distance. Weight = Mass x Acceleration due to gravity
• ﻿Gravity and air resistance
• ﻿Gravity and Air resistance is what makes all different types of forces possible. Free Fall is when the only force acting on  an object is gravity. In free fall the force of gravity alone cause an object to accelerate. Air resistance acts on an object falling through air.An object with a greater surface area experience more air resistance.
• Projectile forces and elastic forces ﻿
• ﻿An object that is thrown is called projectile. Compression and Tension are two types of elastic forces.
• ﻿
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