ICP “Work, Energy and Momentum”

NGSS HS-PS3-1 Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known

Work l work - the product of a net force and the distance through which it acts l work = force x distance l W = Fd l The unit for work is the joule, J. l joule = newton x meter (J = Nm) l joule - the amount of energy expended when a 1N force acts through 1m

Sample Problem l How much work is done on a vacuum cleaner pulled 3.0m by a force of 50N applied on the horizontal? l W = Fd l = 50N x 3m l = 150 Nm l = 150J

Challenge! l An acceleration of 2 m/s 2 acts on a 10kg mass through a distance of 8m. How much work is done? l W = Fd l = ma d l = 10kg x 2 m/s 2 x 8m l = 160 Nm l = 160J

Energy l Energy is measured in terms of the work it does or can do. l Energy has the same units as work, SI - joule. l Like work, energy is a scalar quantity. l Energy is either potential or kinetic. l Potential energy (PE) - energy of position l Kinetic energy (KE) - energy of motion

Kinetic Energy l F = ma l F d = ma d l F d = mv 2 /2 l KE = 1/2 mv 2 l Sample Problem - Calculate the kinetic energy of a 2kg object moving at 5 m/s. l KE = 1/2mv 2 =.5(2kg x (5 m/s) 2 ) l = 25kg m 2 /s 2 = 25J

Potential Energy l The increase in the potential energy of any system is equal to the work done on the system. Gravitational potential energy depends on the mass and height of the object in question. l PE = Fd = mg d = mgh l A 5.0 kg bowling ball is lifted to a height of 1.5m. What is its increase in potential energy? l PE = mgh = 5kg x 9.8 m/s 2 x 1.5m = 73.5kg. m/s 2. m = 73.5J

Work, Energy, and Power l energy - the capacity to do work l energy = work (same units) l power - the time rate at which work is done l P = W / t l The SI unit for power is the watt. l watt - the power required for 1 joule of work to be done in 1 second

Sample Problem l A machine produces 80N of force through a distance of 10m. How much work is done? l W = Fd = 80N x 10m = 800 J l If the work is done in 5 seconds, how much power is used? l P = W/t = 800J/5s = 160 J/s = 160 watts

Momentum and Impulse l momentum - the product of the mass of an object and its velocity l unit for momentum kg m/s l impulse - the product of a force and the length of time during which it acts l unit for impulse N s l Using the units, find the relationship between impulse and momentum.

Newton’s Third Law of Motion l Newton’s Third Law of Motion states that for every action there is an equal and opposite reaction. l Object AObject B l Ft= -Ft l mv= -mv

Law of Conservation of Momentum l The Law of Conservation of Momentum states that the total momentum of an isolated system cannot change. l mv before collision = mv after collision l m 1 v 1 + m 2 v 2 = m 1 v’ 1 + m 2 v’ 2

Sample Problem l A mass of 5.0g moves with a velocity of 20cm/s. This mass collides with a second mass of 10g which is moving along the same line with a velocity of 10cm/s. After the collision, the 5.0g mass is moving at 8cm/s. What is the velocity of the 10g mass after the collision?

Conservation of Matter and Energy l The Law of Conservation of Matter and Energy states “Matter and energy are interchangeable and the total amount of matter and energy in the universe remains constant. l E = mc 2 (c = 3 X 10 8 m/s) l Calculate the energy released when 5g of mass is converted to energy.

Open Response l Suppose you are in a canoe two feet from a boat dock. If you want to get out of the canoe, describe, using Newton’s Laws of motion and any vector diagrams you choose; l A. The effect of jumping onto the ramp. l B. The effect of stepping onto the ramp.