Lecture 1 Newton s laws of motion Newton s rst law every body continues in its state of rest or of uniform motion in a right line unless it is compelled to change that state by forces impressed upon it not intuitive because it looks like the state of rest is the preserved state of motion this is the case because there is friction in the world Newton s second law a force will cause an object of mass to accelerate F ma Newton described the second law in term of impulse F t p Is F ma always the same as F t p They are the same if the mass of the object is constant An example of when the mass of the object is changing is a rocket that is losing fuel Newton s third law to every action there is always opposed an equal reaction or the mutual action of two bodies upon each other are always equal and directed to contrary parts Action reaction pair of forces cannot act on the same body they act on different bodies F F F force on object 2 due to interaction between objects 1 and 2 Group activity string theory A pair of two people pill on the opposite ends of a string Are N and m g third law interaction pairs No they are on the same object so they cannot be interaction pairs The earth is acting two ways on one object A large truck collides head on with a small car During the collision a the track exerts a greater force on the car than the car exerts on the truck b the car exerts a greater force on the truck than the truck exerts on the car c the truck exerts the same force on the car as the car exerts on the truck d the truck exerts a force on the car but the car does no exert a force on the truck Superposition principle F F F Vector decomposition Three forces are acting on an object that is at rest Two of those forces are F 70Ni 20Nj and F 30Ni 40Nj Force physics laws free body diagrams Mass times acceleration mathematical description An object goes from one point in space to another After the object arrives at its destination the magnitude of its displacement is either smaller than or equal to the distance traveled
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