Work and Power 13.1 Work – force is applied to an object and the object moves in the direction as the applied force Work = Force x distance W = F x d **Work is zero when an object is not moving

Measuring Work Joules – SI Units 1 J= 1 N x m = 1kg x m2 / s2

Power Power – the rate at which work is done, or how much work is done in a given amount of time Power = work/time P = W/t Watts – SI units 1 W = 1 J of work in 1 second.

Machines & Mechanical Advantage How do Machines make work easier? Change size of an input force change the direction of the force decrease distance over which force is applied this is – multiplying the force mech. Adv. = output force/input force = input distance/output dist.

Mechanical Advantage output force/input force, or input distance/output dist No units – expressed as a number ** a machine that has a mechanical advantage greater than one multiplies the input force. ** a machine with mechanical advantage less than one increases distance and speed. Can this occur?

Momentum Momentum = mass x velocity P = m v, v = P/m, m=P/v P – momentum M – mass V – velocity (speed + direction) SI units – kg m/s Momentum has direction...indicated by velocity

Momentum Momentum increases as mass and velocity increase If an object’s velocity is zero, it’s momentum is zero Decreasing an objects Momentum will decrease it’s Force

Conservation of Momentum The total amount of momentum in an isolated system is conserved. Momentum is transferred from one object to another in a given collision. Total momentum before objects collide equals the total momentum after the collision.

Impulse The effect of a net force acting on an object (a kind of "moving force") The product of the average net force acting on an object and its duration. J = F Δt Impulse–momentum theorem - the change in momentum of an object equals the impulse applied to it

Impulse

Impulse