Presentation on theme: "Mechanics - Kinematics"— Presentation transcript:
1 Mechanics - Kinematics Define:Displacement – distance & direction from reference point Dx , Dy, Dz.Pos or neg sign gives direction.Velocity – rate & direction object changes in position Dx /t or s/t.sign follows displacement.Acceleration – rate change of velocity Dv /t.Sign give change in vel – not direction.
2 Velocity Average velocity = s tot/ t tot. Instantaneous vel is a limit.Can find from slope of tangent to point.
3 Ex 1: A bus travels north 180 km in 2. 2 hours Ex 1: A bus travels north 180 km in 2.2 hours. It stops for 30 minutes turns and drives 60 km south in 45 min. What is its average velocity in km/h.vav = stot / t tot.34.8 km/h.
4 Kinematics Equations IB Tables pg 6 Uniform/constant acceleration: Dv same increment.u = viv = vfs = displ.a = Dv/t
5 Acceleration of gravity g remarks. Constant/uniform m/s2 on Earth.Negative sign is arbitrary!Often use 10 m/s2 as estimate.Air resistance in atmosphere causes objects to reach terminal fall velocity after falling for a time.Wind/Air resistance increases with speed. Fuel efficiency in cars better at slower speeds.
6 Relative MotionEx 2:You are standing on a railway platform. A is train moving at 25 m/s to the right. On it is a passenger walking to the right at 2 m/s. What is his velocity relative to you?27 m/s.If the velocity of object A, relative to a fixed point is VA, the velocity of object B, relative to the same fixed point is VB, then the velocity of A relative to B is the vector difference: is VA - VB.
7 Ex 3:Car A is traveling 15 m/s and is overtaken by car B which is moving in the same direction at 18 m/s. What is the velocity of car B relative to car A?Vb – Va =3 m/s.What is the velocity of Car A relative to Car B?Va – Vb - 3 m/s
8 Ex 4: A boat heads north across a river 90 m wide Ex 4: A boat heads north across a river 90 m wide. The speed of the boat relative to the shore is 1.8 m/s but the river pushes the boat east at 1.2 m/s. A) What is the speed of the boat relative to the water? B) How far will it land downstream when it arrives at the opposite shore?2.2 m/s60-m.