Momentum can be transfered from one object to another. The value of the momentum of one object is exchanged to other objects during an interaction such that the total momentum of all objects remains the same after the interaction.
Momentum is decreased for one object but increased for the other object by exactly the same amount so the total momentum of the system remains a constant.
Net Momentum(before collision)=Net Momentum(after collision)
How does firing a gun demonstrate conservation of momentum?
A 50 kg girl on roller skates pushes off a 100 kg boy(also on roller skates)and moves at 2 m/s? How fast is the boy moving?
An elastic collision is when objects rebound without lasting deformation or generation of heat M*V=M*V
An inelastic collision is when objects are deformed or heat is generated. In a perfectly inelastic collision, the objects stick together. M*V=(M+M)*v
One object moving at 10 m/s collides with a second object of identical mass standing still. If they stick together , at what velocity do they move?
Conservation of Angular Momentum- the total angular momentum of an isolated system is constant
Angular momentum =mvr
How does an ice skater increase the speed at which they spin?
Energy and Work
Matter and energy make up the universe. Energy is the mover of mass. Energy is abstract and is best viewed as it changes form.
Energy is a quantity(Joule-J) associated with the state of a system
Energy can easily change forms and locations. Energy is both a thing and a process. Sometimes it stored and becomes invisible.
Stored energy(called Potential Energy)can be later released to produce motion, like the chemical energy in your food gives your body the energy to move
Total Energy(in system)=potential energy+kinetic energy+thermal energy
Energy can change from one form to another but is never lost.
Energy is the property of a system that enables it to do work
Work accomplished by energy is measured in Joules(J).Both work and energy are measured in Joules(Newton*Meters)
Work(J)= Force(Newtons) applied thru a distance(Meters) or (f x d). How long in distance you apply a force affects its energy.
A force of 10N is applied to a 20 kg rock for 10 sec and the rock moves 2m. How much work is done?The rock does not move, how much work is done?
Potential Energy(PE) is stored energy. PE is converted into other forms to do work.
Types of Potential Energies(PE).
Chemical-Energy stored in fuels such as foods, gas and batteries. The energy is stored in the bonds between atoms.
Electrical-Energy created by power utilities
Nuclear- Energy(from nucleus of atom)created by converting mass to energy
Elastic - Energy from a coiled spring or drawn bow
Molecules try to keep the same arrangement because of their electrical forces and resist being deformed.
Bouncing Ball Example
Gravitational-Energy stored in an object raised to a height
What happens to the potential energy of an object if you double its height?
How much potential energy does an object have if its mass is 2 kg and it is raised to a height of 3 meters?
Kinetic Energy is energy of motion.
How much KE is in a 5kg rock thrown at 2m/s?
If I am sitting motionless, could I still have energy? If so, what type? Do I have momentum?
Thermal energy is the "ultimate receptor" of energy
It includes sound, heat and light.
When a car's brakes are applied what happens to the kinetic energy?
Why does a swing (pendulum) stop swinging after a short period of time? ie what happened to the energy?
Work-energy theorem- Work equals change in kinetic energy.(FxD=1/2xMxV^2)
If you double your velocity, what happens to your KE?
Two football players collide head on. Player one has a mass of 200kg and runs at 1m/s. Player two has a mass of 100 kg and runs at 2 m/s. Compare their momentums and kinetic energies. Which one wins the battle?
When you are driving at 90 km/hr, how much more distance do you need to stop than if you were driving at 30 km/hr?
Conservation of Energy
(also called the 1st law of thermodynamics)- In a closed system the total amount of energy,including heat, is conserved. In other words, although the kind of energy in a given system can change, the total amount cannot. Energy is converted from one form to another and is not lost.
Energy exchanges drive all interactions
When objects interact energy is transferred from one object to another
Power- The rate of work being done with respect to time. The rate energy is being used.
Power=Work(J)/time(s) - the unit of power is the watt
More power means work is being done more rapidly(ie running up the stairs as opposed to walking), it doesn't necessarily mean that more work is being done.
You move your 50kg mass up 3 flights of stairs(each flight is 5m) in 20 sec. How much work did you do?If ran up the steps in 10 sec instead of walking would you do more work? Would you exert more power? how much?
Exert 100 J in 50 s and your power output is ?
Exert 1 N for a distance of 1 m in 1 s and you deliver a power of ?
Inclined Plane,Wedge and Screw
A machine is a tool that makes work easier. Machines accomplish this by exchanging force and distance.