# Newton’s First Law Newton’s Second law Newton’s Third law.

## Presentation on theme: "Newton’s First Law Newton’s Second law Newton’s Third law."— Presentation transcript:

Newton’s First Law Newton’s Second law Newton’s Third law

 Force is a push or pull  Force can be exerted in different ways  A magnet can exert a force on a paper clip, gravity pulls that paper clip to center of earth, and there is a force that acts on the paper clip when you pick it up

 All forces acting on an object is called the net force  Net force acting on a book might be gravity pulling it toward center of earth and the book pushing up on book. It doesn’t move therefore it is balanced  If two forces are in the same direction, they are added together to form the net force  If two forces are acting in opposite direction, the net for is the difference between the two forces and is in the direction of the larger force

 When two forces are exerted on an object, and the net force is zero their effects cancel each other out and they do not change velocity it is a balanced force  Unbalanced forces are a result when forces on an object are not zero and the effects don’t cancel each other and their velocity changes  Page 551 figure 2

 Sir Issac Newton (1642-1727) developed laws of motion  First law describes how an object moves when the net force acting on it is zero  First law states that an object at rest will remain at rest, or an object in motion will continue in motion unless an outside force acts on it. This occurs when a balanced force is applied  Inertia is an example of Newtons First Law

 Friction is a force that brings all objects to rest  Before Newton people didn’t know about friction or the force that acts in opposite direction of movement  When he realized objects in motion are slowed down by an unbalanced force his first law began to make sense  An object in motion will continue forever unless an unbalanced force acts on it(like friction) or it will remain at rest unless an outside force acts on it

 Static Friction: resistance of objects to begin to move… must overcome static friction to move a book across a table  Sliding friction: resistance of objects once an object is moving. Moves in opposite direction of motion  Rolling friction: less force in opposite direction than sliding friction

 Force: a push or pull on an object  Acceleration occurs any time there is a change of velocity or direction of an object  Newton’s Second law deals with the acceleration of an object that will equal the net force divided by the mass and is in the direction of the net force  A=F net F= ma  m  Unit of force is in Newtons kg*m/s 2

 Gravity is the attraction between any two objects  It is dependent on the size of the objects and the distance between them  Weight: is the size of the gravitational force exerted on an object  It can change as you move farther from center of the earth  W= m (9.8 M/S 2 ) Where 9.8 m/sec 2 is the acceleration rate on earth

 Weight and mass are different  Weight is a force and is measured in newtons  It is a record of the pull of earth’s gravity and can change depending on distance to center of earth  Mass is the amount of matter in an object and doesn’t depend on location

 Speeding up: when an unbalanced force is moving in the same direction as an object …it will speed up  Slowing down: if the unbalanced force is in the opposite direction as objects velocity it will slow down  Can calculate acceleration a=f net /m  Page 559

 Curved path is a result of forces that are neither in same or opposite direction acting on an object

 Circular motion: movement in a circle like a merry-go-round Your direction of motion is constantly changing which also means you are constantly accelerating In order to cause an object to move in circular motion at constant speed, the net force must be at right angles to the velocity Centripetal force is the net force on an object moving in a circle and is toward center of path

 Satellites circle the earth and are kept in motion because of the speed they travel in orbit  They must travel at least 8 km/sec or  29,000 km/h other wise it will fall back to earth

 When an objects moves, there is air resistance  The greater the velocity, the greater the air resistance  Terminal velocity is a result of balancing the gravitational pull and air resistance and the object’s velocity remain the same

 Center of mass is the point in an object that moves as if all the object’s mass were concentrated at that point  The center of mass on an oblong shape is the point if followed in a straight line (Figure 12)

 3 rd law states that for every action there is an equal and opposite reaction  Forces exerted by two objects on each other are often called an action-reaction force  They can be action forces or reaction forces because normally they aren’t equal  Only time they are equal is if forces act on the same object  Bird flying utilizes 3 rd law

 Depending on mass of objects you may not know that there is an equal but opposite reaction ie: jumping off diving board  Rocket launches uses 3 rd law to push rocket upward with gases burning in opposite direction

 Weightlessness is the condition that occurs in free fall when the weight of an object seems to be zero  A falling object is in free fall when the only force acting on the object is gravity and for that split second weightlessness occurs  In orbit all objects are in free fall and falling in a curved path