Push and Pull Newton’s Laws

Newton’s First Law An object at rest remains at rest, and an object in motion continues in motion with constant velocity (that is, constant speed in a straight line) unless it experiences a net external force. Also known as the “LAW OF INERTIA” INERTIA – tendency of an object to maintain its current state of motion

Do these guys have a lot of inertia? Inertia is a relative measurement… –More inertia = MORE MASS –More inertia = harder to CHANGE VELOCITY

Force A force is a push or pull that may change an object’s state of motion. –CONTACT FORCE – requires touching Normal, Tension, Friction –FIELD FORCE – no contact required (“Action over a distance” Gravity (Weight)

A block of wood is placed on a table and is motionless. What forces are acting on it? FgFg FNFN F g = WEIGHT a force pulling any object toward the CENTER OF THE EARTH F N = NORMAL FORCE a reaction force that any object exerts when pushed on

Net Force No NET FORCE on an object = EQUILIBRIUM… either –MOTIONLESS –MOVING WITH CONSTANT VELOCITY A “NET” or “UNBALANCED” force changes an object’s VELOCITY –This means that SPEED AND/OR DIRECTION change –Also called ACCELERATION

Net Force  Acceleration How much acceleration a net force causes an object to have depends on… –amount of FORCE greater force = GREATER ACCELERATION –amount of MASS greater mass = LESS ACCELERATION

Newton’s Second Law The acceleration of an object is directly proportional to the net external force acting on the object and inversely proportional to the mass of the object. Unit of force is the NEWTON (N)

Example A 2.0 kilogram box is pushed with a net force of 10. newtons. What is the acceleration experienced by the box? a = F net / m a = (10 N)/(2.0 kg) a = 5.0 m/s 2

Weight The force with which gravity pulls on an object.

Example What is the weight of an object with a mass of 30 kilograms? F g = mg F g = (30 kg)(9.81 m/s 2 ) F g = kg·m/s 2 or N

Newton’s Third Law “For every action, there is an equal and opposite reaction” FgFg FNFN FgFg FTFT

A firefighter directs a stream of water from a hose to the east. In what direction is the force on the hose? To the WEST Examples

A man getting out of a rowboat jumps north onto a dock. What happens to the boat? It moves SOUTH Examples

A 60 kilogram astronaut pushes against a 120 kilogram satellite with a force of 15 newtons. How much force does the satellite exert on the astronaut? 15 newtons Examples

End of PRACTICE