kinematics notes part 2 - weeblyclogankvhs.weebly.com/uploads/7/8/6/8/78684366/2.0... ·...
TRANSCRIPT
Kinematics Notes Part 2
Vectors, Simple Problems, Graphs of Motion 1
February 17 2017
Thurs Feb 9
Thursday, Feb 9th
• Mark & Hand‐in Toolbox & Sci10
• Begin Kinematics> Chapter 2: Describing Motion
– Displacement, Velocity, Acceleration– Reference Frame & Point
••Math Toolbox Quick Write tomorrow
Kinematics
Unit 1:KinematicsHOW things move...
Chapter 2: Describing Motion
3 Key Words
Displacement
Velocity
Acceleration
Ref Frame & Point
1) Identify the reference frame(Who is the observer? Are they moving?)
2) Choose smart reference points(When/where do we begin measurements?)
Describing Motion
1 02345 1 2 3 4 5
Scalars vs Vectors
Scalars vs Vectors
Magnitude MagnitudeDirection&
AmountQuantity
MeasurementNumber[ ]
Distance: 5 mSpeed: 110 km/hTime: 46 mins
Acceleration: 2 m/s2Mass: 75 kgEnergy: 120 JWork: 80 J
Displacement: 5 m [W]Velocity: 110 km/h [E]
Acceleration: 2 m/s2 @ 45Force: 500 N [down]
Momentum: 45 kgm/s [right]
o
Describing Motion
Qualitative vs Quantitative
Qualitative vs Quantitative
Qualities Quantities
Measurements & Calculations
Diagrams & Descriptions
2468
2 4 6 8
d (m)
t (s)
Describing Motion
Kinematics Notes Part 2
Vectors, Simple Problems, Graphs of Motion 2
February 17 2017
Av Speed vs Velocity
Average Velocity & Speed
vav = ΔdΔt
}Average VELOCITY is defined as total displacement divided by the total time
Average SPEED is defined as the total distance travelled divided by the total time}vav = ΔdΔt
Note: These are TIME averages, not statistical averages. You should NOT add up individual speeds/velocities and divide by how many there are.
dv tav
Ticker tape
Describing MotionA ticker tape machine taps a dot onto a strip of paper as the paper slides through the machine. It can give both qualitative and quantitative information about motion.
+/ Directions
Describing Motion
+
+‐
‐
UP
DOWN
LEFT RIGHT
‐
‐
+
+
When performing calculations using vectors, you must show opposite directions using +/‐ signs. Set them yourself if the question hasn't done it.
Positive Directions: up, right, north, & eastNegative Directions: down, left, south, & west
Types of Velocity
Describing MotionUniform Motion:
Non‐uniform Motion:
Average Velocity:
Instantaneous Velocity:
velocity remains constant; does not change direction or magnitude; instantaneous & average velocities are exactly the same along entire trip. velocity is not constant; changes direction and/or magnitude; object is accelerating.
calculated using initial & final points (displacement); ignores changes along the path/trip.
velocity at one single point in time;calculated from a position‐time graph
Dist vs Disp
Distance & DisplacementExample:A squirrel starts at the curb and tries to scamper straight across a road. It runs out 8 m, sees a dog on the other side of the road and runs back 3 m before being flattened by a truck. What total distance did the squirrel run? What was its displacement?
Reference point?Starting (initial) position?Ending (final) position?
p. 45 #13
Practice Problems: page 45, #1‐3
Kinematics Notes Part 2
Vectors, Simple Problems, Graphs of Motion 3
February 17 2017
Fri Feb 17
Friday, Feb 17th
• Check & Correct Pratice: p.45 #1‐3• Check & Correct P‐T Graphs Sheet
••P‐T to V‐T Graphs•Acceleration
p45 #1
Practice Problems: page 45, #1‐3
Feb 179:29 AM p45 #3a
Practice Problems: page 45, #1‐3
p45 #3bcd
Practice Problems: page 45, #1‐3
Slope = Velocity
vave = ΔdΔt
Slope of a P‐T GraphMotion of a Cyclist
1.3 2.6 3.9 5.2 6.5
12
24
36
48
60
time (s)
position (m[E])
• Slope = rise/run
= Δy/Δx
= Δd/Δt
Kinematics Notes Part 2
Vectors, Simple Problems, Graphs of Motion 4
February 17 2017
PT Graph (Bike)
P‐T to V‐T Graph
AC
B
VT Graph (Bike)
Velocity‐Time GraphsBike Ride Graph
PT to VT Graphs
Going from P‐T to V‐T: Tips1) Calculate the slope along each line segment on your P‐T graph. (v is the same # for the entire line)
2) Make sure the times match up on both graphs.
Bike Ride Graph
Time (s)
Velocity (m
/s [N
])
A
C
B400 800 1200 1600
1
2
‐1
‐2
VT Slope = Acceleration
D
A C
B
E
V‐T Graph & AccelerationPOSITION‐time graph: slope = velocity
(b/c it shows us how position changes over time)
VELOCITY‐time graph: slope = acceleration(b/c it shows us how velocity changes over time)
vave = ΔdΔt
slope = rise/run = Δy/Δx = Δd/Δt
a = ΔvΔt
slope = rise/run = Δy/Δx = Δv/Δt
it's a vector too!
Graphical Analysis
Acceleration:
V‐T Graph: a & d
Displacement:h
vav ΔtΔd Δv
aav Δt
Graphical Analysis
Acceleration:
V‐T Graph: a & d
Displacement:
vav ΔtΔd Δv
aav Δt
Kinematics Notes Part 2
Vectors, Simple Problems, Graphs of Motion 5
February 17 2017
Graphical Analysis
Acceleration:
V‐T Graph: a & d
Displacement:
vav ΔtΔd Δv
aav Δt
Acceleration
a = Δv Δt
Units: m/s = m/s/s = m/s2 s
Acceleration• A vector quantity that describes the rate of change in velocity
o how velocity changes over time
Example:A truck driving 20 m/s East begins to accelerate at 1.5 m/s2.
Time (s)
Velocity (m/s)
0 1 2 3 4 5
Change & Average
vave = ΔdΔt
a = Δv Δt
What does "average velocity" mean?
What does that "delta" really mean??
Vectors
• Velocity vector points in the same direction as the object's motion. • Acceleration vector depends on how the velocity is changing and does not always point in the same direction as the velocity.
• Increasing velocity (speeding up)• vectors point in __________________ direction• must use ________________ sign in your math
• Decreasing velocity (slowing down)• vectors point in _____________________ direction• must use ___________________ sign in your math
Acceleration Vector
Changing Direction
An object can accelerate without changing its speed...
How?
Acceleration is a vector with magnitude and direction.
The direction can change without changing the number.
Acceleration
p70 #1,6,7 p73 #2426
p. 73 #24‐26p. 70 #1, 6, 7
Then sketch P‐T and V‐T graphs of its motion.
Δvaav Δt
Kinematics Notes Part 2
Vectors, Simple Problems, Graphs of Motion 6
February 17 2017
p.70 #1
p. 70 #1, 6, 7
p.70 6,7
p. 70 #1, 6, 7
p73 #2426
p. 73 #24‐26
Uniform/nonuniform Acc
v (m/s)
t (s)t (s)
v (m/s) v (m/s)
t (s)
Uniform & Non‐uniform AccelerationVelocity• v=Δd/t• slope on a PT graph • can be uniform (constant, straight line) • or non‐uniform (changing, curved line)• use a tangent line on a curve
Acceleration• a = Δv/t• slope on a VT graph• can be uniform (constant, straight line) • or non‐uniform (changing, curved line)
> use a tangent line on a curve
Notice that we use the terms constant, average and instantaneous accelerationFig. 2.22 on page 64
t (s)t (s)
a (m/s2)
t (s)
a (m/s2) a (m/s2)
p.64 Figure 2.22
Graph & Slope Comparisons : P‐T, V‐T, A‐T Graphs
v: Const, Ave, Inst
If instantaneous = average, then it's constant.Meaning... that if the velocity at any given point on a line is the same as the average from start to finish, the velocity must not be changing. This is also true for acceleration.
Kinematics Notes Part 2
Vectors, Simple Problems, Graphs of Motion 7
February 17 2017
a: Const, Ave, Inst PT VT Summary P1