Learning from the physic-al world

Surekha Nayani

Physics is everywhere around us – in the working of electric appliances, modes of travel, means of entertainment, medical aids, cooking devices. This is why the subject is better learnt by observing the things around us. Surely, it is very important for physics teachers to explain physics concepts using daily life experiences in order to excite students to explore the subject. Maybe try telling them a story that has physics concepts woven in?

A day in the life of Shailesh Nanisetty
Friction
Shailesh Nanisetty is studying in class X and is a busy bee shuttling between home, school, and sports clubs. Let’s take a look at a day in his life. It is a Sunday. Shailesh wakes up at 7 a.m. and is running late for his cricket academy. He gets ready and puts on his spiked shoes. The spikes on the soles of the shoes increase friction when they touch the ground stopping players from skidding on the smooth surfaces of playgrounds which have less friction. He then takes his cricket kit, which is fixed with four wheels so that it can be pulled along on the ground easily by reducing the friction of the ground. This is called rolling friction. He put the kit on the cycle stand and rode away. The tyres of the cycle have grooves that increase the friction when they come into contact with the road and reduce skidding.

As he was already late, Shailesh began riding fast. In order to increase his speed he bent the upper part of his body. This action led to the reduction of the friction of air on him increasing his riding speed.

Note: At this point in the story you can define friction and also introduce your students to the different types of friction.

Speed and velocity

Shailesh took 10 minutes to reach the cricket ground, which is 3 km from his home. What would be the speed at which he rode the cycle?

If Shailesh’s initial velocity (when riding to the academy) was 10 m/s and the final velocity was 8 m/s, what was his average velocity?

Note: Help students work out these problems by explaining what speed and velocity are. The different units they are measured in, etc.

Distance and displacement

The cricket ground is circular in shape and its diameter is 700 m. Shailesh’s coach asks him to warm up by running around the ground four times.

Note: Let the students calculate the distance Shailesh travels when he runs the four rounds. How does one calculate the distance travelled on a circular ground? This will make for an interesting assignment for the students.

After the warm up, Shailesh begins his practice with the bat. (The handle of his bat is fixed with rubber that has grooves to provide friction, so that the bat doesn’t slip easily from his hands.) He makes a total of 18 runs in 12 balls.

What will the distance travelled by Shailesh be if he has made 18 runs and the length of the pitch is 150 metres? Using the fielders’ positions and their distances from each other you can also introduce your students to the Pythagoras theorem.

After his batting practice, Shailesh starts off with the ball. If Shailesh throws the cricket ball up with a speed of 0.7 m/s, what will be the maximum height the ball can rise up to if the acceleration due to gravity is 9.8 m/s²?

Shailesh then drops the ball from a height of 150 m towards the ground. At the same time, his friend Ritheesh throws his ball up with a 10 m/s velocity, when and where do the two balls meet?

Force

Apart from practicing his cricketing skills, Shailesh also does the routine exercises that are a must for every player. During his exercises he spots a few spring mats in one corner of the ground. Shailesh starts jumping on a mat and finds that he has to apply some force on the mat to jump high. Why do you think Shailesh had to apply force? And what is the impact of that force?

After the exercises are over Shailesh and Ritheesh form two teams. Shailesh bats first. Ritheesh, who is bowling, runs in fast to attain inertia of motion and throws the ball towards Shailesh, who hits the speeding ball with force using his bat in the opposite direction. This action applies force on the ball and changes its direction as well as speed.

After batting two overs Shailesh is caught by Ritheesh, who moves his hand back a certain distance to increase the time of the catch, so that the force acting on his hand is less, i.e., the impulsive force is less (Impulsive Force= force X time). If the time taken to apply force is more the effect of force is less and vice versa.

Note: Ritheesh weighs 65 kg and jumps to express joy at the fall of a wicket. What will the pressure exerted by him on the ground be if his feet occupied an area of 70 cm?

What is force? Think of the everyday situations where we apply force.

Momentum

If a cricket ball thrown with some force accidentally hits a player, he will be badly hurt, but at the same speed if a tennis ball hits a player the impact or pain will be less due to the difference in momentum. The difference in momentum, in this case, is due to the difference in the mass of the two balls. But if the mass is same and the speeds are different, the faster body has higher momentum. This combined effect of mass and velocity is called momentum.

Note: If the mass of the ball is 0.1 kg and it is travelling at a speed of 4 m/s, find the momentum of the ball.

After an hour’s cricket practice, Shailesh goes home by afternoon, has a bath, eats his lunch, and relaxes for some time watching TV. In the evening he completes his school assignments and goes to bed at 10 pm. He wakes up at 5 am the next morning to study for some time and freshens up to go to school by 7.30 am. His busy day starts again.

The author is working as Head of the Department for Science and also as the CBSE Co-ordinator in Delhi Public School, Nacharam, Hyderabad. She can be reached at sulekhanayani@gmail.com.