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.
-----------------------------------------------------------------------------------------
Things to agree on:
1.
2.
3.
4.
4.
5.
6.
Displacement = ∆d= df – di
Time interval= ∆t= tf – ti
For a uniform motion:
The position time graph is a straight line
Slope= displacement/time
= ∆d/ ∆t .
_
Average Speed= s =absolute value of the
slope.
Average speed= distance /time
_
Average Velocity= v=slope.
y- intercept= initial vector position .
A steeper line represents a greater speed
and velocity ( as shows fig 2-20 p:43 on
your textbook)
Application:
1.
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:
1.
Find the average speed, average
velocity in figure 2-21 page 44 in your
textbook.
2.
Draw a corresponding motiondiagram 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.
Application
The figure at the right shows
the motion of a car in a
roundabout. Conclude.
-------------------------------------------------
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 graph
7.
Draw for each object the velocity-time graph.
8.
Find the acceleration for each object
9.
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