FRICTION AND GRAVITY

Two factors that affect the strength of friction- How hard the surfaces push together. The types of surfaces involved.

Which block will have more static friction? Which block will need more force to move?

TYPES OF FRICTION Static Sliding Rolling Fluid

Even very smooth surfaces have irregularities that catch on other surfaces

Static friction Friction that acts on object that are not moving. Extra force is needed to start the motion.

Sliding Friction When two solid surfaces slide over each other.

Rolling friction When a object rolls across the other surface.

Fluid friction When a solid object moves through a fluid. Gases and liquids are both fluids.

GRAVITY The force that pulls all objects toward each other.

The Law of Universal Gravitation: Newton realized that the force of gravity acts on all objects in the universe. Any two object, regardless of size, attract each other. You do not notice the pull because these forces are small compared to the pull of the Earth.

Factors that Affect Gravity Mass is the amount of matter in an object. It is measured in Kg. The more mass an object has, the greater its gravitational force. Distance also affects gravity. The closer the objects the greater the gravitational force between them.

The Earth exerts a force on the moon and the moon exerts a force on the Earth, but the Earth is larger so it has more gravitational pull. If you were on the moon you would weigh less, but your mass would be the same.

Free Fall When the only force acting on an object is gravity. An object in free fall accelerates at 9.8m/s2 In free fall the force of gravity is an unbalanced force, which causes an object to accelerate.

Air resistance Objects falling through air experience a type of fluid friction called air resistance. Air resistance exerts an upward force on the falling object. Air resistance is present when any object passes through air regardless of direction.

Objects with greater surface have greater air resistance. But objects falling in a vacuum fall at the same rate. Air resistance increases with velocity.

Terminal Velocity When objects fall they accelerate, but at some point the air resistance will equal the pull of gravity. This is when the object reaches terminal velocity. The object will not speed up anymore. The object will continue at the constant speed that it has reached at that point . Different objects have different terminal velocity.