2-4 Acceleration When the velocity of an object changes the object is accelerating. Average Acceleration is the change in velocity divided by the change in time

Acceleration is a vector quantity, but in 1D only need + or – to indicate direction

Instantaneous Acceleration The acceleration at any instant, again where time approaches zero. Reminder that acceleration and velocity are not the same thing.

Deceleration Deceleration means that the object is slowing down But, a negative acceleration doesn’t always mean that the object is slowing down. Example??? There is deceleration when ever the magnitude of the velocity is decreasing and then the velocity and acceleration point in opposite directions.

2-5 Motion at Constant Acceleration To simplify; make initial time zero so then t 2 = t (t 2 -t 1 =t) Initial values are not 1, but 0. (v 1 ; v 0 or x 1 ; x 0 ) Rearrange

Because acceleration is constant average velocity is between v and v 0 Combine Rearrange

Begin with Solve for t Substituting into previous equation Solve for v 2

2-6 Solving Problems 1. Read and Reread 2. What object(s) to study and what time interval 3. Draw a diagram 4. Write down known values (Watch Sig Figs) 5. Plan of attack 6. Equations to use 7. Calculations 8. Reasonable? 9. Units

2-7 Falling Objects At a given location all objects fall at the same constant acceleration. (In the absence of air resistance) Acceleration due to gravity 9.80 m/s 2 All equations are the same where a = g = 9.80 m/s 2

2-8 Graphical Analysis of Linear Motion Displacement-time graphs Velocity-time graphs