WORK, ENERGY, MOMENTUM
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| What are the 3 types of potential energy? | gravitational, elastic, electric
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| What does potential energy depend on? | Difference between initial and final heights
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| Stiff springs have smaller / larger "k" value | larger k
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| open system | energy and mass are exchanged with surroundings
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| closed system | energy is exchanged with surroundings but mass is not
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| isolated system | neither energy or mass is exchanged with surroundings
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| Give examples of conservative forces. | gravity, spring force, electromagnetic
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| Define conservative force | -energy removed is same as energy recovered
-force produces same amount of work regardless of path taken
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| What are 2 ways to see if it is a conservative force? | 1.) Sum of work to move particle in a round trip = 0
2.) Sum of work needed to move a particle between two points is same regardless of path taken
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| Formula for conservative forces | KE + PE = KE + PE
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| Work done against a conservative force is conserved in? | Potential Energy
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| What kind of system is the universe? | Isolated system
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| Examples of nonconservative force | friction and air resistance
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| Define nonconservative force | Energy removed cannot be recovered and is no longer available for kinetic energy
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| Is non-conservative force path-dependent? | YES!
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| Does NC / C forces do work? When is mechanical energy conserved? | -Conservative forces do no work -- ME conserved
-Non-conservative forces do work -- ME not conserved
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| Work done against NC force is conserved as? | nothing
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| Conservation of Energy Equation | KE + PE + W = KE + PE + W
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| What does friction affect? | KE only
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| What is work done on a system without friction? | W = Fdcostheta
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| What is work done on a system with friction? | Use Energy Conservation equation
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| Why does conservative force do no work? | Neither energy nor mass is gained or lost by the system
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| What is mechanical energy? | -energy possessed by an object due to its motion/ position
-can either be KE or PE
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| What are kinetic frictional forces? | Friction takes KE of a moving object and transfers it into mvmt of individual molecules on surface of objects in contact with each other
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| How to relate work and friction? | W = -f (friction) * x
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| What are 2 types of energy transfer? | work and heat
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| What is work? | -energy is transferred from one system to another via a force
-system --> surroundings and vice versa
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| What is heat by definition and in relation to KE? | -energy transfer by natural flow from warm --> cold body
-sum of all KE of molecules in an object
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| Is work the same as energy? | NO! --> Work is done on object whenever force acts upon it to cause it to be displaced
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| What do frictional forces change? | change internal and mechanical energy
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| Do perpendicular forces do work? | NO
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| Does work depend on distance traveled? | NO --> only displacement --> path independent
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| 2 equations for power | P = W/t (rate of doing work)
P = Fvcostheta
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| What are the 2 ways for energy to escape a system? | work and heat
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| If system is same temperature as surroundings, where does energy change come from? | work
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| What does it mean to do more work? | greater "a" , greater "v", greater KE, less time to achieve displacement
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| What is positive work? | force and distance applied in same direction
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| What is negative work? | force and distance applied in opposite directions
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| Positive work done on an object | object gains energy
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| Positive work done by object | object loses energy
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| negative work done on object | object loses energy
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| negative work done by object | object gains energy
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| How does work compare between sliding down a frictionless inclined plane and free fall from same height? | SAME
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| Any object with velocity must have? | momentum
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| What is momentum? | measure of a moving object's tendency to continue along its present path
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| What are 2 important points about momentum? | -initial and final momentum always conserved
-vector: momentum is constant in direction and magnitude
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| How can you make it more difficult to change path of a moving object? | increase velocity and mass
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| Conservation of momentum | With no external forces like friction, total momentum before and after collisions are constant
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| Compare momentum and mechanical energy | Momentum is ALWAYS conserved but mechanical energy is NOT ALWAYS conserved (i.e. KE)
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| Compare elastic and inelastic collisions | -Elastic: energy and momentum conserved / no deform
-Inelastic: energy not conserved / momentum conserved / deform
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| What is impulse? | Impact force during collision to change object momentum
--> change in momentum
--> force of collision multiplied by duration of collision
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| Impulse equation | Fdeltatime = change in momentum
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| Do objects always experience the same magnitude of impulse? | YES when momentum is conserved
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| What happens when balls hit each other and lose speed? | lose kinetic energy and thus have inelastic collision
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| What happens when you pull spring away from equilibrium position? | 1.) Restoring force pulls to left --> object accelerates and builds momentum
2.) decelerates once it passes equil. position
3.) force now pulls in opposite direction
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| What is dampened harmonic motion? | lose energy from friction
-energy and amplitude diminish
-frequence and period remain constant
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| What does loss in energy in dampened harmonic motion affect? | KE and PE
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| Why does period stay constant in dampened harmonic motion? | Over time, object will cover less distance, but because its doing it at a reduced average speed, time to complete cycle will remain constant
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| What happens when spring is pushed away from equil position? | PE = max, KE = 0, a = max, v = 0
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| What happens when spring is at equil. position? | PE = min, KE = max, a = 0, v = max
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| When is the tension for a pendulum the greatest? | Bob points down
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| What force opposes tension in a pendulum? | mgcostheta
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| What is tangent to the arc of a pendulum? | mgsintheta
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| Potential energy for a pendulum | PE = -mgL(1 - costheta)
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| What are extrinsic properties? | depends on amount and quantity of material
-mass and energy
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| What are intrinsic properties? | does not depend on amount and quantity of material
-density and pressure
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| A 15eV photon collides with a proton with ionization potential = 13.6 eV. Describe what happens in relation to conservation of energy. | 15eV photon first provides I.E. to unbind electron
--> any excess energy becomes electron's KE
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| Work done by gravity is + / - when it moves down hill and +/- when it moves uphill. | positive and negative
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| Going from PE --> KE, what does object gain? | velocity --> gains momentum
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| Relate frequency and period. | f = 1 / T
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| For work, in what direction must the force be directed? | MUST BE PARALLEL TO MOTION
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| Where must the applied force be directed to change an object's KE? | directed in direction of displacement
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| Does PE depend on the path taken? | NO --> only difference btwn initial and final heights
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| How does work differ in terms of cos/sin between work done on object on ground and one on inclined plane? | -ground = cos
-inclined plane = sin
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| Why do lighter objects experience greater changes in velocity than heavier objects upon collisions? | -Impulse equation: Ft = change in momentum
-same impulse -->greater change in velocity
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| Impulse = | momentum
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| Whether a car comes to rest abruptly or extended over time, how does momentum change? | same change in overall momentum in both
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| When velocity of two objects after a collision decreases, is collision elastic or inelastic? | inelastic --> lose speed and KE
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| Drop a ball and bounces up to same height - what type of collision? | perfectly elastic collision
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| throw a ball at wall and it bounces back with same speed - what type of collision? | perfectly elastic collision
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| Torque | t = r*Fsintheta
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| In torque, what is the optimal positioning for radius and force? | perpendicular!!
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| Trick to solving torque | -indicate direction force is applied
-radius is always perpendicular
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| Mechanical advantage | M.A. = weight / applied force needed to support object
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| Objects with momentum always have...? | KINETIC ENERGY
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| In a collision, what causes a change in momentum? | impulse
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| does impulse = momentum? | NO --> IMPULSE = MOMENTUM CHANGE
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