Presentation on theme: "AP Review Cont.. Forces If there is a force at an angle, make the free body diagram appear level. –Tilt the FBD so that the normal force is pointing straight."— Presentation transcript:
Forces If there is a force at an angle, make the free body diagram appear level. –Tilt the FBD so that the normal force is pointing straight up. –Then separate out the weight (which is now at an angle) into the x and y components –Normal force is the y component of the weight –The x component is the x component of gravity (why a car slides down hill even if there is no other force being exerted on it)
Work and Power Work is measured in Joules (J) –J = N *m W = FcosΘs –F is ΣF unless otherwise specified –F and s MUST be parallel to each other if no angle is mentioned. If there is an angle, it MUST be the angle that will make the force and displacement parallel to each other. –If the force and displacement are perpendicular, there is no work being done on the object. Power is measured in Watts (W) –W = J/s or N*v P = W/t or P = Fv
Energy Mechanical energy is the TOTAL energy of a system (unless your are considering heat too) –ME = KE + PE Conservation of energy: the total energy before equals the total energy after –ME i = ME f –Ke i + PE i = Ke f + PE f If you see mass, height, and velocity in the same problem, it is probably a conservation of energy problem
Energy Energy is measured in Joules (J) Since both work and energy are measure in J, energy is the amount of work done on an object. –W = ΔKE (ΔK on your salmon sheet) –W = - ΔPE (ΔU on your salmon sheet) The initial and final speeds for KE are the actual speeds or overall speed, NOT the speed in the x or y direction. The height for PE is the height from the zero point, wherever the problem states the measurement of the height starts (usually the ground).
Momentum Momentum is like inertia, but in motion p = mv The SI unit for momentum is kg*m/s Impulse is the same as change in momentum and is measured in the same units… J = Δp and since J = FΔt Thru substitution, FΔt = mΔv
Momentum Conservation of momentum: momentum before a collision equals the momentum after the collision p before = p after –Two types of collisions: elastic (bounce off each other with no warping) and inelastic (usually stick together…perfectly inelastic…but they all deform in some way –Collisions in physics are when two or more objects come in contact with each other (coming together or coming apart)
Differentiating types of problems 1.As soon as you see the word force, draw a FBD 2.If you see m, v, and h, it will more than likely be a conservation of energy problem 3.If you see just m and v and there is more than one object involved, it will probably be a conservation of momentum problem.