Kinematics in One Dimension

Velocity and Acceleration

Vocabulary

• Mechanics- Branch of physics that focuses on motion of objects and the forces that cause the motion to change.

• Kinematics- deals with the concepts needed to describe motion without any reference to forces.

• Dynamics- deals with the effect that forces have on motion.

Displacement

• A vector that points from an objects initial position (Xo) toward its final position (Xf)

• To find displacement Xf – X0 = ΔX

Speed

• Speed- The measure of how fast something is moving

• Average Speed = Distance Elapsed Time

*Note* That speed is a scalar quantity

Velocity• Deals with how fast an object moves and

its direction• Average Velocity = Displacement

Elapsed Time• V = Xf – X0 = ΔX

tf – t0 Δt

• Instantaneous Velocity = V= lim Δt 0 ΔX

ΔtMeasurement in m/s

Strategies for Answering Questions

1. Draw/sketch a picture2. List what you are given3. Pick an equation4. Solve the equation for the missing

variable5. Insert numbers into equation

Acceleration• Deals with an objects changing velocity• Average acceleration= change in velocity

change in time• a= ΔV = Vf – Vo

Δt tf – t0

• Instantaneous Accel = a = lim Δt 0 ΔV

Δt• Units of measurement are m/s2

If Velocity and Accel have…

• Same signs – object is speeding up• Opposite signs- object is slowing

down

Constant Velocity

• If V = constant the a = 0 (no acceleration) • Set Xo = 0 when t0 = 0

• X= vt for constant velocity

Constant Accel

• a = constantWhen to = 0 then X = 0 and Vf = V0

• Vf = V0 + at

What is the average acceleration from 0-10 minutes?

What is the displacement and average velocity from 15-30 minutes?

Constant Accel. Equations

Equations Variables

x = VtVf = V0 + at

x= ½ (Vf + V0)t

x = V0t + 1/2at2

Vf2 = V0

2 + 2ax

X V0 Vf a t

Acceleration Due to Gravity

• Read pages 104-105 and (8mins to read / take notes on important info from text about gravity.

• Object is in free fall• Assume no air resistance• a = g = 9.80 m/s2

• Downward direction so –g = -9.80m/s2

• Object moves in y direction