Motion & Forces

Speed & Velocity Speed - the rate of change in position over time (distance/time) Instantaneous speed Average speed How is velocity different from speed? Velocity describes both speed and direction

Change in Velocity What makes an object change velocity?

Force Push or Pull Forces can cause a change in velocity Examples: Gravity Magnetism Friction

Balanced Forces Forces that act on the same object are opposite in direction are equal in size NO MOVEMENT

Balanced Forces Book on table Net force is zero Weight of the book is downward force caused by gravity Table pushes back with an equal and opposite force Net force is zero

Unbalanced Forces CHANGE IN VELOCITY ACCELERATION Forces that are NOT opposite and equal What do they cause? Movement CHANGE IN VELOCITY ACCELERATION

Friction Force that opposes motion between 2 surfaces Depends on the: types of surfaces force between the surfaces

Types of Friction Fluid friction: (Submarine) Static Friction: (Couch Potato) Force between objects at rest Sliding Friction: (Ice skating) Solid surfaces slide over each other Rolling Friction: (Rollerblading) An object rolls over a surface. Fluid friction: (Submarine) An object moves through a fluid

Friction Friction is greater... between rough surfaces when there’s greater force between surfaces (such as more weight)

Lubricant Changes sliding friction into fluid friction Example: Slipping on a mopped floor.

Friction Is friction always bad?

Gravity The attractive force between all objects in the universe. It is what holds our moon in place.

Acceleration of Gravity Near the surface of the earth the acceleration due to gravity is 9.8 m/s/s

Newton’s 1st Law An object at rest remains at rest and an object in motion will continue moving at a constant velocity unless acted on by unbalanced forces.

Newton’s Laws of Motion

Newton’s 1st Law INERTIA tendency of an object to resist any change in its motion increases as mass increases Example: When you are riding in a car. The car stops. You keep moving forward.

Newton‘s 2nd Law If more force is applied, an object will be accelerated _____ more

Force = mass X acceleration Newton’s 2nd Law More force means more acceleration More mass means less acceleration Force = mass X acceleration F = ma

Newton’s 3rd Law For every action, there is an equal and opposite reaction. Forces occur only in pairs Act on different objects Equal and opposite

Newton’s 3rd Law The hammer exerts a force on the nail to the right. The nail exerts an equal but opposite force on the hammer to the left.

Momentum

Terminal Velocity The final speed of a falling object.

Terminal Velocity Air resistance is offsetting the the weight of the object

Forces End

Force Aristotle's idea: For an object to move at a constant speed, a constant force must be applied.

Force Newton’s idea: An object moving at a constant speed will continue at that speed without additional force being applied.

Balanced Forces