2What is Friction?Friction is the resistance to the sliding, rolling, or flowing motion of an object due to its contact with another object. Without friction, an object would continue to move at constant speed forever.
3The strength of the force of friction depends on the type of surfaces and how hard the surfaces push together.Rough surfaces produce greater friction than smooth surfaces.
4Three Types of Friction Static FrictionSliding FrictionFluid Friction
5Static FrictionWhen the force on an object and the friction are balanced.An object is not in motion when there is static friction
6Sliding FrictionA resistance to movement that is created when two things rub together.
7Fluid FrictionThe force that tries to slow objects down when they move through a liquid or a gas. It's also known as "drag", or "air resistance".All gases and liquids are fluids.An airplane and a swimmer both experience fluid friction.
8Ways to Reduce Friction Smooth the surfacePut ball bearings in wheelsReplace sliding with rollingAdd oil or another type of lubricant
9GravityThe attractive force between all objects that have mass
10Universal Gravitation The law of universal gravitation states that the force of gravity acts between all objects in the universe.
11Gravity and Free Fall An object is in free fall when the only force acting on the object is gravity.Free-falling objects do not encounterair resistance.In free fall, the force of gravity is anunbalanced force.
12Calculating Free FallAll objects in free fall accelerate at the same rate – 9.8 m/s² - regardless of their mass.in one second = 9.8 m/s²in two seconds = 19.6 m/s²in three seconds = 29.4 m/s²in four seconds = ________The velocity continues to increase as the object falls.
13Gravity and Air Resistance Most objects falling through air experience a type of fluid friction called air resistance.Air resistance is not the same for all objects.The greater the surface area of the object the greater the air resistance.However, since the elephant has more mass, it has more downward force of gravity and falls faster.
14Weight The gravitational force exerted on an object. Mass: amount of matter in an object.
15Contact vs. Noncontact Forces Contact Force: a push or pull by touchingEx: FrictionNoncontact Force: a force exerted on an object without touching itEx: Gravity