Push and Pull 2-1-1 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

Inertia is a relative measurement… 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)

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

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 = Fnet / m a = (10 N)/(2.0 kg) a = 5.0 m/s2

Weight The force with which gravity pulls on an object.

Example What is the weight of an object with a mass of 30 kilograms? Fg = mg Fg = (30 kg)(9.81 m/s2) Fg = 294.3 kg·m/s2 or 294.3 N

“For every action, there is an equal and Newton’s Third Law “For every action, there is an equal and opposite reaction” FN FT Fg Fg

Examples 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

End of 2.1.1 - PRACTICE