Y10 Physics (0625) 2.2 Lesson 1: Velocity and
acceleration
Introduction
In the previous module, we took our first look at the concept of position and movement.
We learned about speed and how it's calculated, how speed differs from velocity and
how to track motion using distance-time graphs. Although extremely important and
useful concepts, these only cover a small underlying layer of the physics of motion.
In this lesson, we're going to level up and take our knowledge one step further! We'll
begin by taking a look at the concept of acceleration. Once we're comfortable with how
acceleration is described, we'll take a closer look at how it relates to change in velocity
and time taken.
Take some time to review the learning outcomes below. When you feel ready and
comfortable, head through to Section 1 and let's get started!
Learning outcome
Articulate the relationship between acceleration, change in velocity and time taken.
1. Introduction to acceleration
2. Velocity and acceleration
3. Test your knowledge
4. Conclusion
5. Download this lesson
Lesson 1 of 5
1. Introduction to acceleration
Recapping speed and velocity
You'll recall from the previous module that, although closely related, speed and velocity refer to
different things. As speed is a scalar quantity, it is only described by a magnitude (amount). Velocity on
the other hand is a vector quantity, meaning that it is described by both a magnitude (amount) and
direction.
It can often be helpful to attach this information to a real-world scenario. For example, a car could be
described as having a speed of 22 m/s, but a velocity of 22 m/s east. Without describing the direction of
motion, our vector quantity, in this case, velocity, would be incomplete.
Before we expand upon this knowledge, take some time to review the terms in the table below.
Table 1: Definitions for scalar, vector, speed and velocity.
TERM
DESCRIPTION
Scalar
A quantity described by only a
magnitude.
Vector
A quantity described by a magnitude
and direction.
Speed
A scalar quantity describing the rate at
which an object covers distance
(changes position).
TERM
DESCRIPTION
Velocity
A vector quantity describing the rate at
which an object covers distance in a
particular direction (changes position).
Introduction to acceleration
Before we dive too far into the concept of acceleration, take some time to watch the video below. If you
don't understand everything immediately, don't worry! This video is aimed at introducing you to a
couple of more advanced concepts that you will be able to attach information to as we move forward.
These videos will always be here for you to review again as you add to your knowledge and
understanding.
 Remember, the scalar equivalent to velocity is speed. There is no scalar
equivalent to acceleration.
Physics IGCSE: Introduction to acceleration
Video 1: An introduction to acceleration.
Physics (0625)_Y10_T1_M1_C2.2_Video_Transcript.pdf
107.2 KB
Test your knowledge
Great, so you've explored two important equations relating to acceleration! Use your answers from the
last section of the video to complete the following questions.
If it took a person 6 seconds to accelerate from 2 m/s to 5 m/s east, what was
their acceleration?
0.5 meters per second squared
0.5 meters per second squared east
-0.5 meters per second squared east
-0.5 meters per second squared
SUBMIT
An electric skateboard moving west accelerates from 1 m/s to 6 m/s in 100 m.
What is the skateboard's acceleration?
0.175 metres per second squared west
0.175 metres per second squared
-0.175 metres per second squared west
-0.175 metres per second squared
SUBMIT
Some important takeaways
Some key points to take away from this section can be summarised as follows:
Velocity and acceleration are related concepts.
Acceleration describes the rate of change of velocity. In other words, by how much a
velocity has changed in a given period of time.
The SI Unit for acceleration is metres per second squared (m/s2).
A negative acceleration implies that a body is slowing down (decelerating).
There are multiple equations for acceleration, and the equation we use is dependent on
the context of each question.
Lesson 2 of 5
2. Velocity and acceleration
As we touched on in the previous section, velocity describes the rate of change in displacement. We can
see this in equation form in the figure below.
Figure 1: The standard equation for velocity.
Seeing the equation form of a quantity can help us to understand when that quantity describes a rate
of change. If a quantity is defined as a fraction, and 'change in time (Δt)' is in the denominator of that
fraction, then that quantity is a rate of change. We can see a practical example of this in the velocity
equation to the left.
Velocity can reveal a lot of information about how an object is moving. However, after physicists
figured out how to mathematically describe velocity (e.g. the equation above), they soon realised that
it was an insufficient description for motion in the real world.
This is because velocity is very seldomly constant in the real world. That is, objects get faster and slower
over time. Just think about how the velocity of a bicycle might change over a 10km journey. As a result,
physicists needed to find a way to define this change in velocity over time. The solution was
acceleration.
Acceleration is mathematically defined as the rate of change of velocity. We can see the equation for
acceleration in the figure below.
Figure 2: Equation for acceleration.
We can determine the acceleration of a body by dividing the body's change in velocity by the time
taken to achieve that change. We can see this relationship in the equation to the left.
Acceleration in the real-world
Let's take some time to think about how we might calculate acceleration in a real-world scenario.
Consider a scenario in which a car accelerates from rest to a velocity of 10 m/s forwards. This change in
velocity takes place over a time interval of 5 s. How might you calculate the average acceleration of the
car?
Try answering the above question using the knowledge you have acquired throughout this lesson.
When you're comfortable that you've given it your best shot, take some time to move through the
process below and see how close you were to the correct answer.
Introduction
In order to calculate the acceleration of the car in the above scenario, we need to follow a
series of specific steps. Take some time to move through each step of this process. Be
sure to carefully read the description of each step to ensure that you grasp this process
in its entirety.
Step 1
Write down the applicable equation
Figure 3: Write down the equation.
As always in physics, we start by listing our known and unknown variables and using
these to determine and write down the equation we're using.
Step 2
Substitute in the values
Figure 4: Substitute known values into your equation.
After writing down the equation, we substitute in our known values. Be sure to substitute
in round brackets and in the correct order.
Step 3
Simplify
Figure 5: Simplify your equation.
After substituting our values, we can begin to simplify. Sometimes, simplification takes
more than one step. In this case, the simplification is quick.
Provide the final answer in decimal form
Figure 6: Write down your final answer.
After simplification, we can give our final answer. Always provide the answer in the form
instructed by the question. In this example, we can give our answer without rounding
because the quotient divides perfectly. Please remember that we also need to ensure
that we write down the correct units of our answers.
Something that is extremely important to remember is that acceleration is a vector quantity. This
means that it must always be given with both a magnitude and a direction. Make use of the
flashcard below to reinforce your understanding of the difference between an incorrectly and correctly
presented value for acceleration.
Acceleration given
incorrectly
Acceleration given
correctly
Can acceleration be calculated f rom speed?
A question that is frequently asked is whether acceleration can be calculated using speed. The simple
answer is no. However, knowing this answer by heart is less effective than understanding why.
As you know, speed is a scalar quantity, meaning that it is described only by a magnitude (amount).
Therefore, by its nature, we are not able to determine a direction of motion using speed. This implies
that a vector quantity cannot be found through calculations on scalar quantities. Hence, acceleration
can be calculated from velocity but not from speed.
Lesson 3 of 5
3. Test your knowledge
Now that you have reached the end of this lesson, you should have a better idea about how velocity, time taken,
and acceleration are all connected. Answer the questions that follow to make sure that you have grasped the
important concepts.
Question
01/03
Acceleration that is negative implies that:
the body is moving backwards.
the body is slowing down.
the body started rotating in the opposite direction.
the body stopped moving.
Question
02/03
Tau has gotten into a heated debate with a friend. Tau's friend tells Tau that acceleration
can be calculated from the distance that a body moves. Why is Tau's friend incorrect?
I disagree. Tau's friend is correct.
Acceleration can only be calculated from the speed, not the distance.
Acceleration is a vector, and distance is a scalar. There is no way to
extract the direction from a scalar.
Tau's friend should employ the scientific method and measure the
distance multiple times. Once they have a more accurate answer, they
will be able to calculate the acceleration.
Question
03/03
In Section 1 of this lesson, we learned about two equations used to calculate
acceleration. How do we determine which equation to use?
Only one of the equations can make use of speed.
It isn't essential to choose one equation or the other. We can use both
equations at all times.
The equation we use is dependent on the values provided by the
question.
None of the provided answers are correct.
Lesson 4 of 5
4. Conclusion
When physicists found the equations that describe acceleration, they achieved a milestone in human
understanding of motion. By knowing the position, velocity and acceleration of a body, a physicist can
explain many aspects of its movement. This understanding paved the way for Newton's laws and many
more exciting advancements in science.
Before we take a look at how physicists use their understanding of acceleration, it's important that we
have a good grasp of a couple of important concepts. These can be summarised as follows:
Acceleration is described as the rate of change of velocity.
Acceleration is a vector and has no scalar equivalent.
The SI Unit for acceleration is metres per second squared, which is represented as m/s2.
Lesson 5 of 5
5. Download this lesson
Click on the download button below to download this lesson as a PDF!
Physics (0625)_Y10_T1_M2_C2.2_Lesson 1.pdf
1.3 MB