Force And Motion – Session 2

Speed is all about how fast you can travel from one place to another. Imagine you and your friends are riding bikes in the park. If you pedal really fast, your bike will move quickly. As a result you will cover more distance in a shorter time. That means your speed is high. On the other hand, if you pedal slowly, your bike will move more slowly. As a result you will take more time to cover the same distance. That means your speed is low.

Speed is defined as the distance covered in unit time. Let us take an example to understand this. Suppose you see a car moving at sixty kilometer per hour. It means it can cover sixty kilometers of the distance in one hour. Let us say you are riding a bike. How will you measure your speed? Let us understand the formula to calculate the speed.

Imagine you are moving on a bike from point A to point B. To calculate the speed, we need to know about two things. First is the distance covered by the bike. Second is the time it took for the bike to cover that distance. So, the distance and the time are the two things that we should know to calculate the speed. After that we divide the distance by the time.

Let us say that the distance between point A and point B is hundred meters. You have covered this distance in twenty seconds. Can you tell how did you measure the time? Of course you did it with the help of wristwatch or stopwatch.

Now the next step is to divide the distance by the time. The answer we get is five meters per second. Five meters per second is the speed of your bike. Five meters per second means you are covering the distance of five meters in every second. Now suppose you started to paddle more quickly on your bike. It took you five seconds to cover the hundred meter distance. Can you tell what your speed is now?.

We usually measure speed in meters per second or kilometers per hour. We can also measure speed in miles per hour. Hours and seconds are the units of time. Meanwhile, meter, kilometer and miles are the units of distance.

Acceleration is the rate of change of speed over time. Imagine you are riding a bicycle. When you start pedaling and travel from standing-still to moving, you are accelerating. This is because when you start pedaling, your speed is slow. Gradually your speed increases. Acceleration is all about how the speed of something changes over time.

Let us understand this with an example. Suppose you are initially moving from point-A to point-B on bike at the speed of 50 meters per second. After some time you start to pedal harder. Suppose your speed increases to 80 meters per second. Now we can say that you are accelerating because your speed is changing. But how can we calculate the exact rate at which you are accelerating?.

To measure the acceleration, we divide the change in the speed by total time taken. Change in the speed is measured by subtracting the initial speed from the final speed. Initial speed is fifty meters per second. Final speed is eighty meters per second. The change in the speed is thirty meters per second. Then we divide this change in the speed by the time taken by bike to accelerate from the initial speed to the final speed. Suppose it took twenty seconds to accelerate from initial speed to final speed. So the calculated acceleration is 1.5m/s².

Acceleration can happen in two ways. Either you can speed up or slow-down. So, if you are riding a bike and you want to travel faster, you pedal harder. You will accelerate by going faster and faster. But if you want to stop, you press the brakes. The bike slows-down until it comes to a stop. That is also acceleration but in the opposite direction.

Can you tell what is the benefit of understanding speed and acceleration? Understanding speed and acceleration helps drivers on the road gauge appropriate speeds and braking distances. This leads to safer and more efficient travel. Engineers use speed and acceleration calculations when designing vehicles, machines, and structures. These calculations ensure that everything operates within safe limits and performs optimally.

Uniform acceleration is when the speed of an object changes by the same amount in equal intervals of time. It means the object is either getting faster or slower at a constant rate. Imagine you are on a bus. The bus driver gently presses the gas pedal to make the bus move forward. As the bus starts moving, it accelerates at a constant rate. This means that it goes faster by the same amount every second.

Let us say the bus goes at five miles per hour faster every second. After the first second, it is going at speed of five miles per hour. After the second second, it is going at the speed of ten miles per hour. After the third second, it is going at the speed of fifteen miles per hour. The speed increases by the same five miles per hour every second. That is uniform acceleration.

Non uniform acceleration is when the speed of an object changes by different amounts in equal intervals of time. It is like when you are riding your bike on a bumpy road with hills and slopes. Sometimes you pedal faster, and your speed changes quickly. At other times, you pedal slower, and your speed changes more slowly. The speed of bike changes in different amounts every second.

Let us understand it by taking an example of a bus traveling on the road. Suppose you are sitting in a bus. This time there is traffic on the road. The speed of the bus might increase by ten miles per second at one moment. At another moment it might increase by 10 more miles per hour to reach a speed of 20 miles per hour. You can see that the speed of bus is not increasing constantly. It is increasing or decreasing irregularly. This type of acceleration is called non uniform acceleration.