2.4. Speed and Velocity

Good morning everyone! Today, we will discuss speed. Can anyone tell me what speed means?

Is it how fast something moves?

Exactly! Speed measures how fast an object is moving. We calculate it using the formula: Speed = Distance travelled divided by Time taken. This means, if you know how far an object has gone and how long it took, you can find its speed.

So if I run 100 meters in 10 seconds, my speed is 10 meters per second?

That's correct, Student_2! Remember this formula: Speed = Distance/Time. Let's remember it with the acronym ST: S for Speed, T for Time, and D for Distance.

What if I run slower or faster during my run? Does that change my speed?

Great question! The speed can vary if you're not moving at a constant pace, so we will discuss variable speed next.

What if we average it over the whole distance?

Good point! To find average speed, we use Average Speed = Total Distance divided by Total Time. Let’s wrap up this session by remembering: Speed is a scalar quantity, meaning it only has magnitude.

Now, let's transition to velocity. How is it different from speed?

I think velocity includes direction?

Exactly! Velocity is a vector quantity, meaning it has both magnitude and direction. The formula is similar: Velocity = Displacement / Time taken. It’s important to note that displacement is the shortest path from the initial to the final point.

So, if I walk back to where I started, my displacement is zero?

Yes! And thus, your average velocity would also be zero since there’s no change in your position. To help remember, think of the term 'vector' pointing in a specific way; we could use the mnemonic 'D over T' as a reminder for Displacement over Time.

How does that relate to speed again?

Good question! While speed only measures how fast something moves, velocity gives the direction of that movement. This is crucial in navigation and physics where direction matters.

Can velocity ever be negative?

Yes, if an object moves backward from its original position, its velocity can be negative. Remember, velocity can be positive, negative, or even zero, depending on the direction of displacement.

Let’s talk about uniform and variable speed. What do you think uniform speed means?

I think it means going at the same speed the whole time.

Right! Uniform speed means that the speed remains constant over time. In contrast, variable speed means it changes. Think about when you ride a bike and speed up or slow down.

So velocity can also be uniform or variable then?

Absolutely! Uniform velocity entails moving at a constant speed in a straight line, while variable velocity involves changes in speed or direction. Let’s keep these terms in mind using this mnemonic: U for Uniform -> Always the same!

Can I get an example of variable speed?

Consider a car that accelerates from a stoplight and then slows down at a traffic jam; that's variable speed at work! To summarize, speed focuses on how fast and velocity incorporates direction.