Difference between speed and velocity

Objectives

• 1. Define velocity• 2. Differentiate between speed and velocity• 3. Explain the difference between instantaneous

and average speed and velocity• 4. Determine average velocity• 5 Use position-time graphs to determine

instantaneous and average velocities• 6. Write the equation of motion for average

velocity

VELOCITY

Difference between speed and velocity

- Velocity is different than speed.- While speed describes only how fast

an object is moving, velocity gives both magnitude and direction.

- For example, "5 meters per second" is the speed of a moving object ,whereas "5 meters per second east" is a vector.

- Does this sound familiar?• Explain.

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Things to agree on:- Displacement = ∆d= df – di- Time interval= ∆t= tf – ti- For a uniform motion:1. The position time graph is a straight line 2. Slope= displacement/time

= ∆d/ ∆t . _3. Average Speed= s =absolute value of the slope.4. Average speed= distance /time _

4. Average Velocity= v=slope.5. y- intercept= initial vector position .6. A steeper line represents a greater speed and

velocity ( as shows fig 2-20 p:43 on your textbook)

Application:

7. Find the average speed, average velocity and initial vector position of the moving object whose motion is represented by the figure at the right.

Write an equation representing the motion.

APPLICATION

• Find the average speed, velocity and initial vector position of the motion represented by the following position-time graph.

• Write the equation of the motion

• Solve question p 45 no.27

Look at the following motion diagrams representing the motion of two cars

1. Plot the position-time graph for each car.

2. Find the slope for each line.-------------------------------------

3. What is the speed for each motion--------------------------------------

4. What is the velocity for each motion.---------------------------------------

5. Find the initial vector position for the two cars. Write the equation of motion for each car.---------------------------------------

6. Where and when the two cars meet?------------------------------------------------

Application:7. Find the average speed, average velocity

in figure 2-21 page 44 in your textbook.8. Draw a corresponding motion- diagram

for the moving object.

Difference between velocity and speed

Conclusion:To have a constant velocity, an object must have :

1. constant speed 2. motion in a constant direction.

Constant direction means a straight line and constant orientation.

ApplicationThe figure at the right shows the motion of a car in a roundabout. Conclude.

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Conclusion

• Speed is how fast an object moves. It only has a magnitude. It is a scalar In a position-time graph of a linear uniform motion, the average speed is the absolute value of the slope.

• Velocity is the speed of an object in a given direction. It has a magnitude and direction. It is a vector. In a position- time graph, the average velocity is equal to the slope.

• Application:Solve Questions p:45 no.35,26 & 27 + p53 no.49-51

The following Diagram represents the motions of two moving objects. Answer the below questions.

1. What type of motion is represented by each object?

---------------------------------------2. Calculate the average speed of

each object----------------------------------------3. Do the two objects have the

same velocities? Explain.

-----------------------------------------4. Calculate the instantaneous

speeds for each object between 0.1 s and 0.2 s.

-------------------------------------------------5. Conclude.-------------------------------------------------

Difference between average velocity and instantaneous velocity

Average velocity _

• Average speed= s = distance

time__V= displacement/time= ∆d/∆t• Is the average velocity

during the whole path• It has the direction of the

motion

Instantaneous velocity• Represents the velocity at a

particular moment.

• It has the speed and direction of the moving object at a certain moment.

Assessment:Solve questions II and III

Uniformly accelerated motion

•Velocity is not kept constant•Velocity –time graph is a straight line•Slope= velocity change= time interval =∆v=aceleration (m/s2) ∆t• equation: _ V= at+ vi

Application:Find the equation of velocity of the motion represented in the figure, Find velocity at t= 1 s.Find the time when velocity is 12 m/s.

Application

• Find the equation of velocity of the motion represented in the figure.

• Find velocity at t= 1 s.• Find the time when

velocity is 12 m/s.

Look at the following diagram and answer the below questions

1. Find the average speed of object A and B-----------------------------------2. Represent the average velocity for A and B by

corresponding vectors.3. Find the instantaneous velocities at instant 0.1

and 0.5 s for every object. Conclude.------------------------------------------4. What type motion is represented by each

object?--------------------------------------------5. Calculate the value of the velocities at instant

0.1-0.5 s for each object-----------------------------------------------6. Draw for each object the position-time graph7. Draw for each object the velocity-time graph.8. Find the acceleration for each object9. Write the equation of motion for object A-----------------------------------------------------------------10. Write the equation of each object.-----------------------------------------------------------------11. Write the equation of motion of object B------------------------------------------------------------------

Uniformly accelerated motion

• Velocity is not kept constant• Velocity –time graph is a straight line• Slope= acceleration

Equation of a Linear uniform motion

• Position time graph line of best fit: -------------• Position-time relationship: ----------------------• Equation: ----------------------------------

where: the average velocity represents --------and the initial vector position represents -------

So the equation would be:Application: Find the equation of the the motion represnted by the

previous graph.Solve page 53 no 54

For next time:

• Continue solving the worksheet• Download PowerPoint presentation on your

macbook from wikispaces.• Quiz next lesson sections 1.3 and 2.2• Homework page 53 no.56 & 57