FORCE AND MOTION I Change in velocity acceleration Q: What causes acceleration? An interaction that can cause an acceleration of a body is called a force. The force is said to act on the body

Isaac Newton (1642-1727) Provided an understanding of the relation between force and acceleration. It does not apply to all situations -Objects moving close to speed of light -Physics of the atomic scale objects such as electrons

Newtonian Mechanics Three primary laws Newton’s First Law Before Newton it was thought force is needed to keep a body moving Galileo

Newton’s First Law If no force acts on a body, it’s velocity can not change If it is at rest, it stays at rest. If it is moving with a velocity, it will continue tobe moving with the same velocity. FORCE The force needed to accelerate a body of 1 kg mass with acceleration of 1 m/s2 is 1 Newton (1 N) Q: Is force a vector quantity? Yes, it has both magnitude and direction.

Q: If two or more forces acting on a body, what happens? There will be a net force or resultant force determined by adding the forces vectorially.

Newton’s First Law If no net force acts on a body (Fnet=0), then the body’s velocity can not change no acceleration. An inertial reference frame is one in which Newton’s first law holds. Mass

Newton’s Second Law Mass is an intrinsic characteristic of a body. Mass is a scalar quantity. The mass relates a force on the body to the resulting acceleration. Newton’s Second Law The net force on a body is equal to the product of the body’s mass and the acceleration of the body. Vector sum of all the forces act on the body.

Units?

The Gravitational Force

The Normal Force When a body presses against a surface the surface pushes on the body with a normal force N that is perpendicular to the surface.

Tension The force along the cord in these cases are called Tension Force

Newton’s Third Law Newton’s third law: When two bodies interact, the forces on the bodies from each other are always equal in magnitude and opposite in direction. They do not cancel each other because they are acting on different bodies.