physics honors lecture a & b days 08/31/15 & 09/1/15 motion in 1d

Physics Honors Lecture A & B Days08/31/15 & 09/1/15

Motion in 1D

Agenda

•Motion in 1D?•Displacement•Velocity•Problems

What is motion in 1D

•What is motion?

What is motion in 1D

•What is 1D?

• It is Not

What is motion in 1D

•So then what dimension are these in?

1D 2D

2DCircular

3D

Motion in 1 - D

•Simplest form of Motion•Train on tracks

•Frame of reference - a coordinate system for specifying the precise location of objects in space

Motion in 1 - D

•Choose your frame of reference so that the problem is in easiest coordinates

• Choose the origin for t=0 sec• For 1 D, always along axis

Motion in 1 - D

•Choose your frame of reference so that the problem is in easiest coordinates

• Choose the origin for t=0 sec• For 1 D, always along axis

Displacement

•Displacement •“Change in” position

•Direction matters - positive or negative

•Not always equal to distance traveled

Displacement

∆ 𝑥=𝑥 𝑓 −𝑥 𝑖Positive = + “positive displacement”

Right , Up or Towards You

Negative = - “negative displacement”

Left, Down or Away from You

Displacement

•Class example

10

“positive displacement”

Displacement

•Class examples

∆ 𝑥=−4− (+10 )=−14

Right = + “positive displacement”

Displacement

•Class examples

Left = - “negative displacement”

∆ 𝑥=−7− (−4 )=−3

Displacement

•Class examples

Positive = + “positive displacement”

∆ 𝑥=0− (−7 )=+7

Displacement vs. Distance Traveled

•Total Displacement from Previous examples•All that matters is the starting and final position

•What about the distance traveled?

Displacement vs. Distance Traveled

•Distance traveled takes into account every path taken

Distance traveled ( or just distance) is neither positive nor negative•Distance is a Scalar value

Displacement vs. Distance Traveled

•Scalar -a quantity that is fully described by magnitude alone•We will run into more scalars later

•Displacement is a vector - a quantity that is fully described by both “magnitude and direction”

Velocity Answers how this displacement took place. •Did it happen slowly or fast

Is speed = velocity?No

Average Velocity v. Average Speed

• Vector – magnitude and direction• Positive or negative –

left or right • Not slowing down

or speeding up

• Scalar – just a number (magnitude)• Is NOT positive or negative

Examples ProblemsHeather and Matthew walk eastward with a speed of 0.98 m/s. If it takes them 20 min to walk to the store, how far have they walked.

Write down the given values. Write down what we are looking for.Write down the equation we need to use. Convert units.Manipulate equation. Input number with units. Calculate answer with correct units.Clearly mark answer.

Examples ProblemsIf it takes you 9.5 min to walk with an average velocity of 1.2 m/s to the north from the bus stop to the museum entrance. What is your displacement.

Write down the given values. Write down what we are looking for.Write down the equation we need to use. Convert units.Manipulate equation. Input number with units. Calculate answer with correct units.Clearly mark answer.

Examples ProblemsSimpson drives his car with an average velocity of 48.0 km/h to the east. How long will it take him to drive 144 km on a straight highway?

Write down the given values. Write down what we are looking for.Write down the equation we need to use. Convert units.Manipulate equation. Input number with units. Calculate answer with correct units.Clearly mark answer.

Let’s try and do this …

• Lightning Strike

•Homework – P. 66 #51, 58, 64, 68, 70, 78, 80, 82, 83, 84, 97, 100