physics 121
DESCRIPTION
Physics 121. 2. Motion in one Dimension. 2.1 Reference Frames and Displacement 2.2 Average Velocity 2.3 Instantaneous Velocity 2.4 Acceleration 2.5 Motion at Constant Acceleration 2.6 How to Solve Problems 2.7 Falling Objects 2.8 Graphs of Linear Motion. Speed. - PowerPoint PPT PresentationTRANSCRIPT
![Page 1: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/1.jpg)
Physics 121
![Page 2: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/2.jpg)
2. Motion in one Dimension
2.1 Reference Frames and Displacement
2.2 Average Velocity
2.3 Instantaneous Velocity
2.4 Acceleration
2.5 Motion at Constant Acceleration
2.6 How to Solve Problems
2.7 Falling Objects
2.8 Graphs of Linear Motion
![Page 3: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/3.jpg)
Speed
Speed = Distance / Time
v = d / t
![Page 4: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/4.jpg)
Example 2.1 . . . From a Distance
If you are driving 110 km/h along a straight road and you look to the side for 2.0 s, how far do you travel during this inattentive period?
![Page 5: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/5.jpg)
Solution 2.1 . . . From a Distance
v = d/t30.6 m/s = d / 2.0 sd = 30.6 m/s x 2.0 sd = 61 m
Given: v = 110 km/h t = 2.0 s Solve for: d
110 km/h = 110 km/h x 1000 m/km / 3600 s/h
110 km/h = 30.6 m/s
Formula v = d/t
But first … convert speed (v) into m/s!!!
![Page 6: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/6.jpg)
Distance and Displacement
Displacement measures the change in position of an object. Also, the direction, in addition to the magnitude, must be considered.
Distance and Displacement can be very different if the object does not proceed in the same direction in a straight line!
![Page 7: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/7.jpg)
Example 2.2 . . . Around the block
A BC
A car travels East from point A to point B (5 miles) and then back (West) from point B to point C (2 miles).
(a) What distance did the car travel?(b) What is the car’s displacement?
![Page 8: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/8.jpg)
Solution 2.2 . . . Around the block
A BC
A car travels East from point A to point B (5 miles) and then back (West) from point B to point C (2 miles).
(a) Distance traveled is 7 miles(b) Displacement is 3 miles East
![Page 9: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/9.jpg)
Speed and Velocity
Velocity = displacement / time
•Car A going at 30 m.p.h. EAST and car B going at 30 m.p.h. NORTH have the same speed but different velocities!
•A car going around a circular track at 30 m.p.h. has a CONSTANT SPEED but its VELOCITY is CHANGING!
![Page 10: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/10.jpg)
Example 2.3 . . . Speed and Velocity
John Denver negotiates his rusty (but trusty) truck around a bend in a country road in West Virginia.
A. His speed is constant but his velocity is changing
B. His velocity is constant but his speed is changing
C. Both his speed and velocity are changing
D. His velocity is definitely changing but his speed may or may not be changing
![Page 11: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/11.jpg)
Solution 2.3 . . . Speed and Velocity
John Denver negotiates his rusty (but trusty) truck around a bend in a country road in West Virginia.
A. His speed is constant but his velocity is changing
B. His velocity is constant but his speed is changing
C. Both his speed and velocity are changing
D. His velocity is definitely changing but his speed may or may not be changing
![Page 12: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/12.jpg)
Example 2.4 . . . On the road again!
A BC
A car travels East from point A to point B (5 miles) and then back (West) from point B to point C (2 miles) in 15 minutes
(a) What is the speed of the car?(b) What is velocity of the car?
![Page 13: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/13.jpg)
Solution 2.4 . . . On the road again!
A BC
A car travels East from point A to point B (5 miles) and then back (West) from point B to point C (2 miles).
(a) Speed is 28 mph(b) Velocity is 12 mph East
![Page 14: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/14.jpg)
Instantaneous Velocity
• Instantaneous means measured at a given instant or moment (“Kodak moment”). Experimentally, this is virtually impossible. One must measure the distance over an extremely short time interval
• Average means measured over an extended time interval. This is easier to measure.
![Page 15: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/15.jpg)
Speed and Velocity . . . revisited!
• Speed = distance / time
• Velocity = displacement / time
• For translational motion (straight line) in the same direction, speed equals velocity!
• Speed is an example of a SCALAR quantity. Only the magnitude (amount) is specified without regard to the direction
• Remember to specify the magnitude and the direction for displacement and velocity. These are VECTOR quantities
![Page 16: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/16.jpg)
Acceleration
Acceleration is the rate of change of velocity
a = ( vf - vi ) / t
![Page 17: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/17.jpg)
Example 2.5 . . . Uniformly accelerating car
When the traffic light turns green, the speed of a car increases uniformly from vi = 0 m/s at t = 0 s to vf = 18 m/s at t =6 s
(a) Calculate the acceleration(b) Calculate the speed at t = 4 s(c) Calculate the distance traveled in 6 s
![Page 18: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/18.jpg)
Solution 2.5 . . . Uniformly accelerating car
a = (Vf - Vi ) / ta = (18 - 0) / 6a = 3 m/s2
Vf = Vi + a tVf = 0 + 3x4Vf at 4s = 12 m/s
Vave = (Vf + Vi ) / 2
Vave = (18+0)/2
Vave = 9 m /s
Vave = d / t
9 m/s = d / 6 s
d = 54 m
![Page 19: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/19.jpg)
Example 2.6 . . . Motion in one dimension
• Is the speed constant at t=10s?
• When is the acceleration zero?
• When is it slowing down (decelerating)?
• What is the acceleration at t=7s?
![Page 20: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/20.jpg)
Solution 2.6 . . . Motion in one dimension
• Is the speed constant at t=10s? No
• When is the acceleration zero? 13 s < t < 42 s
• When is it slowing down (decelerating)? t > 42 s
• What is the acceleration at t=7s? 1 m / s2
![Page 21: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/21.jpg)
Equation Summary for uniform acceleration (No Jerks Pleeeease!)
Vave = d / t
Vf = Vi + a t
Vave = (Vf + Vi) / 2
d = Vi t + 1/2 a t2
Vf2 = Vi
2 + 2ad
![Page 22: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/22.jpg)
Example 2.7 . . . Driver’s not a jerk!
A car accelerates from a stop light and attains a speed of 24 m/s after traveling a distance of 72 m. What is the acceleration of the car?
![Page 23: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/23.jpg)
Solution 2.7 . . . Driver’s not a jerk!
(24)2 = 0 + (2)(a)(72)a = 4 m/s2
Given: Vi = 0 Vf = 24 m/s d = 72 m Solve for: a
Formula Vf2 = Vi
2 + 2ad
![Page 24: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/24.jpg)
Example 2.8 . . . Free Fall
Acceleration due to Earth’s gravity is 9.8 m/s2
(a) A cat falls off a ledge. How fast is it moving 3 seconds after the fall?
(b) What is the distance traveled by the unfortunate cat?
![Page 25: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/25.jpg)
Solution 2.8 . . . Free Fall
Vf = 0 + (9.8)(3)Vf = 30 m/s
Given: Vi = 0 a = 9.8 m/s2 t = 3 s Solve for: Vf d
Formula Vf = Vi + a t d = Vi t + 1/2 a t2
d = 0 + (1/2)(9.8)(3)(3)d = 44 m
![Page 26: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/26.jpg)
Example 2.9 . . . Granny’s Orchard
Big apple is twice as big as Little apple. Both fall from the same height at the same time. Which statement is correct?
A. Both reach the ground at about the same time
B. Big reaches the ground way before Little does
C. Little reaches the ground way before Big does
![Page 27: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/27.jpg)
Solution 2.9 . . . Granny’s Orchard
Big apple is twice as big as Little apple. Both fall from the same height at the same time. Which statement is correct?
A. Both reach the ground at about the same time
B. Big reaches the ground way before Little does
C. Little reaches the ground way before Big does
![Page 28: Physics 121](https://reader035.vdocument.in/reader035/viewer/2022062222/56815b15550346895dc8c52e/html5/thumbnails/28.jpg)
That’s all folks!