Forces and Motion Notes 6th Science Lesson 2 Notes in English

6th Science Lesson 2 Notes in English

2] Forces and Motion

Introduction

When we open the door, kick a football, lift our school bag, all involve motion and there is some push or pull.

Motion and Rest

• Suppose there is a book on your table right in the middle.“it is not moving; it is at rest”.
• If you push the book to one side of the table to clear space for keeping your notebook, then the book is moving.
• When the book was at the same place with respect to the table, the book was at rest; but when it was pushed from one place on the table to another place, you say it was moving.
• When there is a change of position of an object with respect to time, then it is called motion, if it remains stationary it is called rest.

How things move?

• When we kick a ball it moves. When we push the book on the table, it moves. When a bullock pulls the cart moves. Motion occurs when the object is pulled or pushed by an agency.
• In daily life, we pulled out water from the well, with bucket or “the animal pulls a bullock cart”. It is a person or animal, that is an animate agency that does the pushing or pulling.
• Sometimes we see a tall grass in the meadow dancing in the wind, a piece of wood is moving down a stream. What pushes or pulls them? We know that blowing wind and flowing water is the cause.
• Sometimes the push or pull can be due to the inanimate agency.

Contact, Non-Contact Forces

• In all the above cases, the force is executed by touching the body. so, these type of force is called Contact Force.
• Mysteriously ripen coconut falls to the ground. What pulls it to the ground? We would have heard of the ‘force of gravity’ of Earth. Gravity pulls the ripen coconut from the tree to the ground.
• Bring a magnet near the small iron nail. Suddenly the nail jumps into the air and sticks with the magnet. Observe that the magnet and the nail did not touch each other.
• Still, there was a pulling force that made the nail to jump towards the magnet. In these two examples, the force is applied without touching the object. Such forces are known as “non-contact forces”
• Forces can be classified into two major types; contact and non-contact forces. Wind is making a flag flutter, a cart pulled by a bullock are contact forces. Magnetism, gravity are some examples of non-contact forces.

What happens when we apply a force on an object?

• If you push a book on the table. The book moves. Application of force in an object results in motion from a state of rest.when a batsman hit a ball The ball is already in motion, but with the strike, the speed of the ball increases.
• Moreover the direction of the ball changes.Application of force on object results in a change in its speed and change in its direction. Crush a balloon, apply force on roti dough, pull a rubber band.
• In these cases the shape of the object change on application of force. Application of force in object results in expansion or contraction.
• In a nutshell, the applied force is an interaction of one object on another that causes the second object to move from rest, or speed up, slow down, stop the motion, change the direction, compress or expand.

Forces can

1. Change the states of body from rest to motion or motion to rest.

2. Either change the speed or direction or both of the body.

3. Change the shape of the body.

That is its motion was ‘rotational’ and then ‘circular’ ‘straight line or linear’ and later ‘oscillatory’. Throw paper aeroplanes or paper dart. Watch its fl ight path when you throw it at an angle. The path curves i.e the paper fl ight is moving ahead but direction is changing while moving such paths are called curvilinear.

Periodic and non- periodic motions

A fly buzzing around the room is a combination of all these and fl ight path is zigzag.

You can classify the motion according to the path taken by the object.

a. Linear– moving in a straight line, like a person walking on a straight path, free fall.

b. Curvilinear – moving ahead but changing direction, like a throwing ball.

c. Circular -moving in a circle, swirling stone tied to the rope.

d. Rotatory -The movement of a body about its own axis, like a rotating top.

e. Oscillatory -coming back to the same position after a fixed time interval, like a pendulum.

f. Zigzag (irregular) – like the motion of a bee or people walking in a crowded street.

Speed Vs Slow ?

• Motion repeated in equal intervals of time is called as periodic motion.Revolution of the moon around the earth is periodic but not oscillatory.
• However, the children playing in a swing is both periodic and oscillatory.Compared to walking, cycling is fast, but a bus is faster than a cycle. The aeroplane is much faster than a bus.
• So, slow or fast is a relative concept which depends upon the motions we are comparing.

Speed

The distance travelled by an object in unit time is called average speed of the object.

If an object travelled a distance (d) in time (t) then its

Average speed (s) is = distance travelled / time taken = d/t.

In science we generally use SI units. In SI units the unit of distance is metre and the unit of time is second. So, the SI

unit of average speed is metre/second.

Speed = distance travelled / time taken

(s = d/t)

s = d/t or st = d

therefore the distance travelled is speed × time.

Uniform and non-uniform motion

• Suppose a train leaves Thiruchirapalli and arrives at Madurai. Is the train travelled in an uniform speed? First, the train was stationary. When the train left the station, the motion was slow and only after it left some distance that it gathered speed.
• After that it slowed down while crossing bridges and stop at intermediate stations for passengers. Finally, as the train approached Madurai, again, it slowed and finally came to a halt.
• That is the speedwas not same all through the journey time. That is the speed was non-uniform. This motion is said to be non-uniform motion.However, in between the journey, there may have a stretch where in the train might have been going at a constant speed.
• During that interval the train was moving at uniform speed, that is uniform motion.If an object covers uniform distances in uniform intervals then the motion of the object is called Uniform Motion.
• Otherwise the Motion is called Non-Uniform Motion.

Multiple Motion

The tyres rotate and make a rotatory motion, but the cycle as such moves forward in a linear path.

Science Today – Robot

• Robots are automatic machines. Some robots can perform mechanical and repetitive jobs faster, more accurately than people.
• Robots can also handle dangerous materials and explore distant planets. The term comes from a czech word, ‘robota’ meaning ‘forced labour’.
• Robotics is the science and study of robots.

What Can Robots Do?

• Robots can sense and respond to their surroundings. They can handle delicate objects or apply great force-for example, to perform eye operations guided by a human surgeon, or to assemble a car.
• With artificial intelligence, robots will also be able to make decisions for themselves.

How Do Robots Sense?

• Electronic sensors are a robot’s eyes and ears. Twin video cameras give the robot a 3-D view of the world.
• Microphones detect sounds. Pressure sensors give the robot a sense of touch, to judge how hard to grip an egg.
• Heavy luggage built-in computers send and receive information with radio waves.

Artificial Intelligence

• Artificial intelligence attempts to create computer programs that think like human brains.
• Current research has not achieved this, but some computers can be programmed to recognize faces in a crowd.

Can Robots Think?

• Robots can think. They can play complex games, such as chess, better than human beings. Humans are conscious-we know we are thinking-but we don’t know how consciousness works.
• We don’t know if Robots can ever be conscious.

Nanorobotics

• Nano-robots or nanobots are robots scaled down to microscopic size in order to put them into very small spaces to perform a function.
• Future nanobots could be placed in the blood stream to perform surgical procedures that are too delicate or too difficult for standard surgery.
• Imagine if a nanobot could target cancer cells and destroy them without touching healthy cells nearby.

More to Know:

1. Usain Bolt crossed 100metre in 9.58 seconds and made a world record.

2. Oscillations at Greater Speed

When the oscillation is very swift, it is called as vibration. Fast oscillations are referred to as vibrations.

3. Forces are push or pull by an animate or inanimate agency.

4. Aryabatta, an ancient Indian astronomer, said that like the banks of the river appear to move back to a person in a boat floating gently in a river, the night sky studded with stars appear to move from east to west while Earth rotates from west to east.

Problem:

1. If a ship travelled at a speed of 50 kmph and it sailed for five hours, how much distance it had travelled.

s = 50 kmph; t = 5 therefore s × t = 50 kmph × 5 h = 250 km

If we know the speed and distance travelled we can compute the time taken.

s = d/t that is t = d/s

time taken = distance travelled / speed

2. Suppose a bus travels at a speed of 50 kmph and has to cover a distance of 300 km. How much time will it take?

t = d/s that is 300 km/50 kmph = 6 h.