phy 01 01 present ppt
TRANSCRIPT
Physics
1
Unit 1: Motion in One Dimension
Motion …
Kinematics in One Dimension
The source of content for this course is www.physicsclassroom.com
Physics
2
Unit Objectives/LessonsStudents will be able to…1. One Dimensional (1-D) Kinematic quantities and
relationships; solve basic 1-D motion problems• Displacement and Velocity quantities and relationships• Acceleration quantities and relationships
2. 1-D Motion by Graphical Means using linear motion graphs: displacement (d) vs. time (t) and velocity (v) vs. time (t)
3. Free Falling body kinematics using primary kinematic equations
4. 1-D Motion by Algebraic Means using primary kinematic equations
Unit 1: Motion in One Dimension
Physics
3
Kinematics
Science of describing the motion of objects using words, diagrams, numbers, graphs, and equations
Unit 1: Motion in One Dimension
Physics
4
Lesson Objectives
Students will be able to…• Understand the 1-D Kinematic concepts of
displacement, time, velocity and acceleration• Understand scalars and vectors as
measurement quantities• Solve basic 1-D motion equations
Lesson 1: 1-D Kinematics Intro
Physics
5
Scalar vs. Vector – measurement quantities
scalar: have magnitude (value), but no direction.Examples: time, mass, distance.Mass has a number value (like 58 kg), but we don't give it a direction (like “East”).
vector: have magnitude and directionExamples: velocity, force, displacement.Force has a magnitude (like 37 N) and a direction (like "pushed to the left").
Lesson 1: 1-D Kinematics Intro
Physics
6
Displacement and Time
Essential information needed to describe the motion of an object
Displacement of an object is always measured from some reference point
- usually “zero” as the motion’s starting point
Lesson 1: 1-D Kinematics Intro
Physics
7
Displacement vs. Distance
Distance is a scalar quantity which refers to "how much ground an object has covered" during its motion.
Displacement is a vector quantity which refers to "how far out of place an object is"; it is the object's overall change in position.
Lesson 1: 1-D Kinematics Intro
Physics
8
Displacement vs. Distance
Distance ?Displacement ?
Lesson 1: 1-D Kinematics Intro
A
Physics
9
Displacement vs. Distance
Example 1
Lesson 1: 1-D Kinematics Intro
Set Up Table – Time, Distance & Displacement
Physics
10
Displacement vs. Distance
Simple formula for calculating the displacement of an object is…
Δd = df - di
• Δ symbol is the Greek letter “delta” and means “a change in…”• Subscript “f” and “i” stand for final and initial
Lesson 1: 1-D Kinematics Intro
Physics
11
Displacement vs. Distance
Example 2: A truck going east passes a mark on the road that says 150m, and then passes another one 10s later that says 450m. Determine the truck’s displacement during the 10s period.
Δd = df - di =
Lesson 1: 1-D Kinematics Intro
Physics
12
Displacement vs. DistanceExample 3: You start walking home from school. After walking 1.5 km East, you get a phone call from your mom asking if you can meet her at the mall. You will have to turn around and walk 2.3 km West. Determine your distance and displacement to get to the mall.
Distance =
Displacement =
Lesson 1: 1-D Kinematics Intro
Do Worksheet Problems – Distance & Displacement
Physics
13
Velocity vs. Speed
Speed is a scalar and refers to “how fast an object is moving”. e.g. “we drove at 65 km/hr.”
Velocity is a vector and refers to "the rate at which an object changes its position.”e.g. “we drove at 65 km/hr east.”
Lesson 1: 1-D Kinematics Intro
Physics
14
Average VelocityThis leads to the first major formula, the calculation of average velocity:
vavg = average velocity (m/s)Δd = df - di = displacement (m)Δt = tf - ti = time (s)
Why is this considered the “average” velocity?
Lesson 1: 1-D Kinematics Intro
t
dvavg
Physics
15
Average Velocity
Example 4: I try to run the 100m race to break the world's record. Unfortunately, it takes me 16.83s to complete the run. Determine my average velocity.
This is my average velocity. What was my speed?Was is constant for 100m?
Lesson 1: 1-D Kinematics Intro
t
dvavg
Physics
16
Average Velocity
Example 5
Lesson 1: 1-D Kinematics Intro
Set Up Table – Time, Speed & Velocity
Physics
17
Average Velocity
Note that in the example, the displacement and the velocity were positive numbers.
• Positive and negative tell you direction with respect to the reference point (these are vectors!)
• Positive velocity means you are moving forward, to the right, or up, while negative means you are going backwards, to the left, or down
Lesson 1: 1-D Kinematics Intro
Physics
18
Average Velocity
Example 6: Look back at Example 3. Determine your speed and velocity if the walk took you one hour and ten minutes. Use standard units and the correct sig digs.
speed =
velocity =
Lesson 1: 1-D Kinematics Intro
Physics
19
Uniform Motion
Lesson 1: 1-D Kinematics Intro
Physics
20
Uniform Motion
Assume object is moving at the same velocity the whole time.• If velocity is always the same, it has a constant
velocity - the object is not accelerating• Also call this uniform motion• Uniform motion is the easiest kind of motion to
describe and measure
Lesson 1: 1-D Kinematics Intro
Physics
21
Instantaneous Velocity
In real life we often have to deal with an object traveling without uniform velocity.
An example is driving with a friend in a car.
Instantaneous velocity is the velocity of an object at one moment of time
Lesson 1: 1-D Kinematics Intro
Do Worksheet Problems – Speed & Velocity
Physics
22
Acceleration
Lesson 1: 1-D Kinematics Intro
Physics
23
Acceleration
Acceleration:- describes the change in velocity over time- it is a vector – magnitude and direction.
In real life we typically deal with an object traveling without uniform velocity.
An example is driving with a friend in a car.
Lesson 1: 1-D Kinematics Intro
Physics
24
Acceleration
Lesson 1: 1-D Kinematics Intro
Physics
25
Average AccelerationThis leads to the second major formula, the calculation of average acceleration:
aavg = average acceleration (m/s2)Δv = vf - vi = velocity (m/s)Δt = tf - ti = time (s)
Why is this considered the “average” acceleration?
Lesson 1: 1-D Kinematics Intro
t
va avg
Physics
26
Average Acceleration
Example 6: A car moving at 50km/h accelerates to 60km/h in 7.0 seconds. Determine its acceleration.
Lesson 1: 1-D Kinematics Intro
Physics
27
Negative Acceleration
In physics, acceleration is not always an increase in velocity. It can also be a decrease in velocity.
• Since acceleration is a vector, it has direction
• We call a decrease in velocity of an object traveling forward a negative acceleration
Lesson 1: 1-D Kinematics Intro
Physics
28
Negative Acceleration
The general RULE OF THUMB is:
If an object is slowing down, then its acceleration is in the opposite direction of its motion.
Lesson 1: 1-D Kinematics Intro
Physics
29
Negative Acceleration
Lesson 1: 1-D Kinematics Intro
Physics
30
Negative Acceleration
Lesson 1: 1-D Kinematics Intro
Physics
31
Negative Acceleration
Example 7: You are walking down the street when you see an enormous, 112kg pickle rolling towards you at 12 m/s. Surprised, you jump in front of it and begin pushing on it until you finally bring it to a stop 17.5s later. Determine the acceleration of the pickle.
Lesson 1: 1-D Kinematics Intro
Physics
32
Instantaneous Acceleration
In real life we often have to deal with an object traveling without uniform acceleration.
An example is driving with a friend in a car.
Instantaneous Acceleration is the acceleration of an object at one moment of time
Lesson 1: 1-D Kinematics Intro
Do Worksheet Problems - Acceleration
Physics
33
Lesson 1: 1-D Kinematics Intro
Summary
Vocabulary: Formulas: - Displacement Δd = df - di
- Average velocity- Instantaneous velocity- Initial & Final velocity- Uniform motion- Average acceleration- Instantaneous acceleration- Vector & scalar
t
dvavg
t
va avg