2 What is Friction?Friction is the resistance to the sliding, rolling, or flowing motion of an object due to its contact with another object. When a moving object comes in contact with another object, friction is the opposing force that slows or stops the moving object.
3 Without friction, an object would continue to move at constant speed forever. The 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.
4 Without friction you could not WriteDrive a carFly an airplaneWhy not?
5 Rolling Friction Static Sliding Friction Fluid Friction Four Types of FrictionRolling FrictionStaticSliding FrictionFluid Friction
7 Rolling FrictionRolling friction is friction that occurs between surfaces in motion in which one of the surfaces is a wheel, roller, or ball.Examples:Riding a bike – tires and groundBowling – ball and lane
13 Fluid 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.
14 Ways to Reduce Friction Smooth the surfaceReplace rolling with slidingAdd oil or another type of lubricant
16 Gravity 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.
17 Calculating 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.
18 Gravity, Free Fall, and Projectile Motion An object that is thrown is called a projectile.If there is no air resistance, an object that is dropped and an object that is thrown are both in free fall.Without the force of air resistance, both objects will hit the ground at the same time.
19 Gravity 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.