Energy and Momentum Conceptual Physics 11/16/2018

Impulse(J) – the change in momentum, J=Ft or J=Δp Momentum(p) – inertia in motion, p=mv, units are kg m/s, it is a vector quantity Impulse(J) – the change in momentum, J=Ft or J=Δp demo of momentum: use two carts, two bar masses and the track to show how objects move when they collide Use the example of the space shuttle coming in to land and the large S-curves it makes for impulse. Also use the boxer example for impulse – roll with the punches. Also use the car’s dash as an impulse example – it gives so the impulse is large. 11/16/2018

Elastic Collisions – when objects hit each other and bounce back Law of Conservation of Momentum – the momentum of any system remains the same unless an outside force acts on it Elastic Collisions – when objects hit each other and bounce back Show again how momentum is conserved on the track with the cars. Use the bumpers on the cars to demonstrate elastic collisions. Use a racquet ball to show elastic collision with the floor. 11/16/2018

Inelastic Collisions – when two objects hit each other and stick together Work (W) – force through a distance where the force and distance are in the same direction; unit is Joules(J); W=Fd Use the carts with the velcro ends to show inelastic collisions. Use two students with one picking up a paper clip and the other carrying a large weight across the room to demonstrate that force and distance must be in the same direction for any work to be done. Be sure to mention walking down a hallway (W=0 J) and walking up stairs (W ≠ 0 J). 11/16/2018

Energy (E) – the ability to do work measured in Joules (J) Power(P) – the rate work is done; P=W/t; unit is watts; 750 watts=1 horsepower Energy (E) – the ability to do work measured in Joules (J) Potential Energy (PE) – the energy of position; PE=mgh measured in Joules Use a light bulb as the example of power. Mention the power exerted by a person walking up stairs. Drop a book to show PE. 11/16/2018

Mechanical Energy (ME) = KE+PE measured in Joules Kinetic Energy (KE) – the energy of motion; KE=1/2 mv2 measured in Joules Mechanical Energy (ME) = KE+PE measured in Joules Work-Energy Theorem – whenever work is done, energy changes; W=E Throw a ball slowly and then quickly to show KE. 11/16/2018

Law of Conservation of Energy – energy can neither be created nor destroyed only changed from one form to another Use the two metal balls to show how kinetic energy can change to thermal energy. Slide a book across a desk and talk about the kinetic energy changing into heat and sound – same for bouncing a ball. Mention that thermal energy is the measure of the vibration of the molecules in an object and is measured as the object’s temperature. Discuss how the molecules in gases, liquids and solids behave differently and how temperature (addition of thermal energy) changes the molecules inside each. Show track with ball where PE goes to KE. 11/16/2018