A change in position relative to some reference point during a period of time. Motion.
18
• A change in position relative to some reference point during a period of time. Motion
-
Upload
sam-sandles -
Category
Documents
-
view
216 -
download
1
Transcript of A change in position relative to some reference point during a period of time. Motion.
• A change in position relative to some reference point during a period of time.
MotionMotion
• Rate at which an object moves
• Speed = distance/time
• Units: m/sec, km/hr, mi/hr.
SpeedSpeed
d s t
• Instantaneous Speed – speed at a given instant.
• Average Speed = ∆ distance/ ∆ time. Describes speed of motion when speed is changing.
• Constant Speed – speed that doesn’t change.
Types of SpeedTypes of Speed
Speed ProblemsSpeed Problems
What is the speed of a cyclist who travels 50 meters in 25 seconds?
S = d/t
You are in a car traveling an average speed of 60 km/hr. The total trip is 240 km. How long does the trip take?
t = d/s
50 m/25 s 2 m/s
240 km/60 km/hr 4 hrs.
Distance -Time GraphsDistance -Time GraphsD
ista
nce
(m
)
Time (sec)
Time (sec)Time (sec)
Time (sec)
Dis
tance
(m
)
Dis
tance
(m
)
Dis
tance
(m
)
• Speed in a given direction.
• Uses: Navigation (airplanes, ships), weather, etc.
• Vector quantity – represented graphically by arrows ( ).– Length =
magnitude– Arrowhead =
VelocityVelocity
direction
• If you row a boat upstream at 10 km/hr and the river has a downstream velocity of 5 km/hr, you are actually moving at what velocity?
Velocity ProblemVelocity Problem
10 km/hr upstream
5 km/hr downstream
5 km/hr upstream
=
• Rate of change in velocity.
• Really a description of “how fast you can go in a certain amount of time”.
• Good acceleration is being “quick to change”.
AccelerationAcceleration
• Examples: speeding up (+ acc.), slowing down (- acc.), or changing direction.
• Acc. = final velocity – original velocity/time.
• Units: m/sec/sec
• Represented by a Velocity – Time Graph
AccelerationAcceleration
Velocity vs. Time GraphsVelocity vs. Time Graphs
Time (sec)
Velo
city
(m
/s)
Time (sec)
Velo
city
(m
/s)
Time (sec)
Velo
city
(m
/s)
Time (sec)
Velo
city
(m
/s)
• A car increases its speed from 60 km/hr to 80 km/hr in 4 seconds. What is the car’s acceleration?
Acceleration ProblemAcceleration Problem
80 km/hr – 60 km/hr
4 sec.
1st second – 65 km/hr
2nd second – 70 km/hr
3rd second – 75 km/hr
4th second – 80 km/hr
5 km/hr/sec.
Acc = Δ velocity
time
Rates of Motion TableRates of Motion Table
Rates Definition Equation Unit Graph
Speed
Velocity
Acceleration
• Acceleration on an object caused by gravity.
Gravitational AccelerationGravitational Acceleration
Falling ObjectsFalling Objects
• Free fall – considers only gravity & neglects air resistance.
• All falling objects accelerate at the same rate, regardless of their masses.
- 9.8 m/sec/sec or 32 ft./sec/sec. on
earth.
- velocity increases 9.8 m/s each
second.
- distance fallen – increases
mathematically
• Instantaneous speed vf = vi + at
• Distance fallen d = vit + ½at2
• Average speed v = vi + vf
Uniform Motion EquationsUniform Motion Equations
2
Objects Thrown Straight UpObjects Thrown Straight Up
Graphing Free FallGraphing Free FallD
ista
nce
(m)
Time (sec)
velo
city
(m
)
Time (sec)
• Air resistance noticeably alters the motion of things like falling feathers or pieces of paper.
• Less noticeably on more compact objects. e.g. stones, balls
Air Resistance on Falling Objects
Air Resistance on Falling Objects
