Speed, Velocity, Acceleration

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# Speed, Velocity, Acceleration - PowerPoint PPT Presentation

Speed, Velocity, Acceleration. BY: BRIANNA SHIELDS. DO NOW- Get hmwk out!. Complete the physics handout on front counter. GOAL. To interpret graphs and solve word problems involving speed, velocity, acceleration and momentum. Motion. Change in position during a time period

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### Speed, Velocity, Acceleration

BY: BRIANNA SHIELDS

DO NOW- Get hmwk out!
• Complete the physics handout on front counter
GOAL
• To interpret graphs and solve word problems involving speed, velocity, acceleration and momentum
Motion

Change in position during a time period

3 types of motion

Speed

Velocity

Acceleration

Speed

1. Definition: Rate at which an object moves

2. Formula: Distance divided by time (d/t)

3. Units: m/s or km/s

Speed

4. Constant speed - speed that doesn’t change

5. Average speed- add speeds, divide by total number

Speed

6. Graphs:

Time: x-axis

Distance: y-axis

Constant speed

Changing speed

Copy samples of these into your notebook

Cheetah Speed Graph
• In one second how far had the cheetah run?
• In three seconds how far had the cheetah run?
• What was the cheetah’s average speed?
Bicycle Graph
• After one hour how far had she traveled?
• Two hours?
• Three hours?
• Four hours?
• Is she traveling at a constant speed? Why/why not
• During which hours was her speed the greatest?
• What does the flat line on the graph indicate?
Calculating Speed: Example
• If 2 runners ran the same distance (10km) but one completed it in 3600 seconds and the other in 2800 seconds, what were each of their average speeds?
• 1: d/t 10km/3600 sec .00278 km/sec
• 2: d/t 10 km/ 2800 sec .00357 km/sec
• Runner 2 has greatest average speed!
Calculating Speed: Example
• Spirit of Australia, a hydroplane boat, made speed records by traveling 239 miles in 0.75 hours (45 minutes). What is it’s record breaking speed?
• d/t 239 miles/ 0.75 hr
Velocity

1. Definition: Describes speed plus direction (n, s, e, w)

2. Formula: D/T plus direction

3. Units: m/s or km/s, north, south, east or west

Velocity

4. Velocities can be combined

Add velocities when in same direction

Velocities in opposite direction= subtract

Velocity

5. Graphs:

Time: x-axis

Distance: y-axis

(same as speed graphs but also has direction)

Calculating Velocity: Example
• If a runner is running east at 10 m/s sec, what is her velocity?
• 10 m/s east
Calculating Velocity: Example
• If you’re rowing a boat downstream at 16 km/hr, and the curren is moving at 10 km/hr. How fast does the boat “look” like it’s going to someone on shore? (Draw a picture too!)
• 16 + 10
• 26 km/hr downstream
Calculating Velocity: Example
• If you’re rowing a boat upstream at 15 km/hr, against a current moving at 8 km/hr. What is you’re actual velocity to an observer on the shore?
• 15-8
• 7 km/hr upstream
Calculating Velocity: Example
• If you are running up an escalator at 2 steps per second and its moving downward at 3 steps per second, what is the total velocity? In what way are you moving?
• 3-2
• -1 (you are actually moving backwards, down the escalator, although you’re running up it)
Acceleration

1. Definition: Rate of change in velocity

Speeding up, slowing down, changing direction

2. Formula: Final velocity minus original velocity, divided by time

3. Units: m/s/s or km/s/s

Acceleration

4. Increasing velocity - positive acceleration

5. Decreasing velocity - negative acceleration- deceleration

Acceleration

6. Graphs

X- axis- time

Y-axis- distance

Object must be changing velocity

Line, is smooth and curved (not straight)- “changing line”

Acceleration Graph- Race Car
• 1. From 0-1 sec how far did the race car go?
• 2. From 1-2 sec?
• 3. From 2-3 sec?
• 4. Is the car accelerating or decelerating? Explain.
Calculating Acceleration: Example
• A roller coaster’s velocity at the top of a hill is 10m/s. Two sec later it reaches the bottom of the hill with a velocity of 26 m/s. What is the acceleration of the roller coaster?
• Vf-Vo

T

26-10

2

8 m/s/s

Calculating Acceleration: Example
• A roller coaster’s velocity at the bottom of a hill is 25 m/s. Three seconds later it reaches the top of the next hill, moving at 10 m/s. What is the deceleration of the roller coaster?
• A = Vf-Vo

T

A = 10-25 = -7.5 m/s/s

2

Calculating Acceleration: Example
• A car is traveling at 60 km/hr. It accelerates to 85 km/hr in 5 seconds. What is the acceleration of the car?
• A = Vf-Vo

T

A = 85-60 = 5.0 m/s/s

5

Momentum

1. Definition: Depends on object’s mass and velocity

Related to force upon impact

2. Formula: Mass x velocity

3. Units: Kg.m/s

Calculating Momentum: Examples
• If 2 football players are running at the same velocity towards an opponent. Player 1 weighed 170 lbs, player 2 weighed 250 lbs. Who is going to move the opponent farther? Why?
• Since both players were traveling at the same velocity, the larger player will have more momentum, thus, moving the opponent farther
Calculating Momentum: Examples
• Why would it be harder to stop a car traveling at 65 miles/ hr than it is to stop one traveling at 35 miles/hr? Explain
• If they have approximately the same mass, the faster car will gather more momentum, according to the equation: momentum = mass x velocity
Calculating Momentum: Examples
• What is the momentum of a 0.3 kg bluejay running into a window while flying at 17 m/s?
• momentum = mass x velocity
• = 0.3 x 17 = 5.1 kg m/s
Websites
• Fear of Physics
Assignment
• Write the homework assignment into your agenda:
• Practicing Motion