Changing Motion

Constant Acceleration Pre Lab

• What relationship is being researched?• What are the constraints?

Constant Acceleration Pre Lab

2if tt

TimerPosition

(m)Time(s)

Midpoint time Slope(m/s)

1       NA

2        

3        

4        

5        

6        

7        

8        

9        

10        

N/A

Constant Acceleration Post Lab

Position vs. Time GraphWhat are the trends in the position vs. time graph? • Steepness• Slope

Position vs Time

Slope Interpretation • The slope of the graph is: a. increasing, decreasing or

constant

b. positive, negative, or zero

c. distance, velocity, or acceleration• What type of velocity is the

slope?Average – Constant – Instantaneous

• Calculate the velocity.

Constant Acceleration Post Lab

Position vs. Time Graph

What are the trends in the position vs. time

graph?

• Steepness

• Slope

c. distance, velocity, or acceleration

The slope of the graph is:

a. increasing, decreasing or constant

b. positive, negative, or zero

Slope Interpretation

Calculate the interval velocities

 V0-1 =

 

V1-2 =

 

V2-3 =

 

V3-4 =

 

V4-5 =

t

xv 50

V3-4 =

 V4-5 =

 Calculate the average velocity. 

t

xv 50

txv 50

interval velocities.

1. The slope of a straight-line connecting two points that lie on a linear position vs. time graph.

Average Velocity Constant Velocity

Instantaneous Velocity

interval velocities2.   The slope of a straight-line connecting two points that

lie on a non-linear position vs. time graph.

Average Velocity Constant Velocity Instantaneous Velocity

interval velocities

3. The slope of a straight-line tangent to a point that lies on a non-linear position vs. time graph.

Average Velocity Constant Velocity

Instantaneous Velocity

Define Acceleration• Acceleration is any change in the

velocity of an object with respect to time.

• The difference between two velocities divided by the time for the change.

• Mathematically: a = (V2 –V1 )/t

Constant Acceleration Post Lab

Velocity vs Time GraphWhat are the trends in the velocity vs. time graph?

 Derive: vf = vo + at

Velocity vs Time

Example Problems Example #1

A car increases its velocity from 4 m/s to 25 m/s in 5.5 seconds. Find the car’s acceleration?

G: vi = 4 m/s

v = 25 m/s

t = 5.5 s

U: acceleration (a)=_____?

E: vf = vi + at

S: See Overhead

S: See Overhead

Example #1

Find the car’s displacement while speeding up.

A car increases its velocity from 4 m/s to 25 m/s in 5.5 seconds.

G: vi = 4 m/s

v = 25 m/s

t = 5.5 s

U: displacement (d)=_____?

E: d = vit + 1/2at2

S: See Overhead

S: See Overhead

Example Problems Example #1

G: vi = 25 m/sv = 0 m/st = 50 s

U: acceleration (a)=_____?E: d= vit + 1/2at2

S: See OverheadS: See Overhead

The car’s driver then applies the brakes and stops the car in 50 meters.

Find the car’s acceleration

A car increases its velocity from 4 m/s to 25 m/s in 5.5 seconds

Example Problems Example #1

A car increases its velocity from 4 m/s to 25 m/s in 5.5 seconds.

Find the time to stop the car.

G: vi = 25 m/s

vf = 0 m/s

U: time (t)=_____?

E: v = vi + at,

vf2 = vi

2 + 2ad,

d = vit = 1/2at2

S: See Overhead

S: See Overhead

A golf ball dropped from a 10-meter tall building strikes the ground at 12.5 m/s and rebounds at 5 m/s. Find the ball’s acceleration if the time of impact equaled 0.025 seconds.

G: d = 10 m vi = -12.5 m/s (direction) vf = 5 m/s (direction) t = 0.025 s

U: accelerationE: vi = vf + at S: See OverheadS: See Overhead

Example Problems Example #2

The red car is waiting at a red light. The green car timing the light perfectly, drives by the red car just as the light turns green. The green car is traveling at a constant speed of 15 m/s while the red car having started from rest accelerates at 2 m/s2. Find when and where the red car catches up to the green car.

 G: v0R = 0 m/s

vg = 15m/s

aR = 2 m/s2

 U: t = _______d = ______

E: d = v0Rt = ½ at2

d = vgt S: see overhead S: see overhead

Example Problem Example #3

What’s the reference point?  

How are positive and negative defined?

Carts and Tracks Pre Lab

What are the relationships between velocity and acceleration in terms of speeding up - slowing down?

How is the sign (+,-) related to speeding up or slowing down?

If the sign of the velocity and acceleration are the same does the object speed up or slow down?

If they are opposite does the object speed up or slow down?

Carts and Tracks Pre Lab

Sign Relationships - Complete the chart below by placing either a +, - and/or zero in each box.

Carts and Tracks Post Lab

Motion Velocity Acceleration

Speeding Up    

Speeding Up    

Slowing Down    

Slowing Down    

Constant Velocity

   

Speeding Up from Rest

   

Remaining at Rest   

 18. An object will only speed up if the acceleration and velocity are:

Lab Part IV: Summarizing all the Scenarios

14. In ALL 6 of the scenarios the acceleration of the cart was directed:15. If the acceleration of an object is positive then the object could:16.  If the acceleration of an object is negative then

the object could: 17. An object will only slow down if the acceleration and velocity are:

Lab Part IV: Summarizing all the Scenarios

19. In scenario C when the object was at the highest point on the ramp the velocity of the object was:_______ even though the acceleration was _______ . 20. In scenario F when the object was at the highest point on the ramp the velocity of the object was _______ even though the acceleration was_______ . 21. In general, the velocity of an object can be zero and the acceleration could be ___________, ___________ or zero.

Part V: Extension22. An object is thrown straight up into the air. As it rises after leaving the thrower’s hand it speeds up / slows down. This indicated that the object is accelerating upward / downward. 23. After reaching the top of its motion it falls and begins to speed up / slow down. This indicated that the object is accelerating upward / downward. 24.At the top of its motion the velocity of the object is ____ and its acceleration is ________.

25. Whenever an object moves only due to the influence of the gravitational force it accelerates ___________ .

Graph of Motion Interpretation

Complete the chart as viewed from the overhead.