Light is form of energy and is very important in all aspects of our lives. In the absence of light plants would not able to grow as they require sunlight to prepare their food and in absence of plants, animal and human would have nothing to eat.
We see with our eyes but we cannot see anything when there is no light. We have noticed that in complete darkness no object is visible to us.
Light travels from a light source.
Sun is the main source of natural light. Other forms of natural light are other stars and moon. Star provides very less amount of light at night because they are very far from earth compared to sun. Moon, especially full moon provides little light at night but light from the moon is just light reflected from the sun. Some animal also emit their own lights such as glow-worms, fireflies and some fish.
Source of artificial light are burning wood, candles, earthen lamps. Candle are made of wax, oil and wick are used in lamp to burn. Now days we use electric bulb, tube and lamp as source of light.
Luminous bodies are those which emit light of their own such as sun, stars and bulb. Non luminous bodies are those which do not have their own light such as moon, book etc. Non luminous object are visible to us when light from luminous object falls on them.
Light travels in a straight line in the form of rays. It travels very fast at the speed of 300,000 km in a second! Light does not bend, it can only be blocked. Light continue to travel in straight line until it hits something else.
It is evident from shadow formation that light travels in straight line.
When light rays hits on any surface, it bounces back (it reflect back). We are able to see objects because light rays enter our eyes after bouncing off rough surface. A rough surface reflects or bounces off light in all directions whereas smooth and polished surface bounces off light in one direction. Therefore, mirrors are good reflectors.
Material that allows light to pass through them in straight lines is called transparent material. Object on other side of transparent material is clearly visible. Example: glass, crystal, clear plastic.
Material that allows some light to pass through them is called translucent material. Object on other side of translucent material is not clearly visible. Example: Tissue paper, frosted glass, colored glass, butter paper, colored plastic.
Material that does not allow any light to pass through them is called opaque material. Example: wood, metal, stone, our body.
Shadow is formed when light is not able to pass through an opaque object. When an opaque object come in the path of the light, the light falling on that object cannot reach the other side, therefore, that particular region becomes dark. The rest of the area is lit as there is nothing to stop the light from passing through.
The object must be opaque or translucent to make a shadow. Opaque objects make dark shadows and translucent objects make faint shadows. A transparent object will not make any shadow, as all light will pass through it.
If we bring an object closer to the light source, the shadow becomes bigger as it blocks more of the light rays and if we take an object away from light source, the shadow becomes smaller as it blocks less amount of light.
The Sun casts long shadows in the morning and evening as the Sun is lowest in the sky. The Sun casts the shortest shadows at midday, when the Sun is highest in the sky.
Lateral inversion is the reversal of image when placed against plain mirror. It may also be referred as “mirror image”. This implies that object on the right side appears on the left side in the mirror.
Sound is created when something vibrates and sends waves of energy (vibration) into our ears. The vibrations travel through the air or another medium (solid, liquid or gas) to the ear. The stronger the vibrations, the louder the sound. Sounds are fainter the further you get from the sound source.
Sound changes depending on how fast or slow an object vibrates to make sound waves. Pitch is the quality of a sound (high or low) and depends on the speed of the vibrations. Different materials produce different pitches; if an object vibrates quickly we hear a high-pitched sound, and if an object vibrates slowly we hear a low-pitched sound. Sounds are usually a mixture of lots of different kinds of sound waves.
Sound is the term to describe what is heard when sound waves pass through a medium to the ear. All sounds are made by vibrations of molecules through which the sound travels. For instance, when a drum or a cymbal is struck, the object vibrates. These vibrations make air molecules move. See the fact file below for more information about sound.
Sound is energy that is made by vibrations. When any object vibrates, it causes the particles to move in the air. The air particles then bumps into each other and then bump into others. This continued bumping cause a sound wave. Therefore, ears hear the sounds. When these particles move fast, a high volume of sound is formed. And then, when these particles move slowly, a low volume of sound is produced.
If the human ear is within the range of the vibrations, a sound can be heard.
Sound waves are also known as pressure waves because the wave moves the particles along its passa
The ear is not the only detector people and animals have. Sound waves can even be felt by different parts of the body. Sometimes you can feel the vibrations thunder makes while you are actually hearing it.
Musical sounds are composed of regular and uniform sound vibrations. Music can be described as a beautiful or expressive arrangement of sounds. Noises are formed by irregular and disordered sound vibrations.
If you fear noise, then you have Acousticophobia.
If you fear music, then you have Melophobia.
Stringed instruments are played when fingers or a bar are pressed down on the strings. This pressure changes the string’s length, causing them to vibrate at different frequencies and make different sounds. Shortening a string makes it sound higher, while lengthening a string can produce a lower sound. Strings also produce different sounds depending on how thick they are.
In wind instruments, there is a reed – a thin piece of wood inside the mouthpiece, which vibrates when air travels over it. The keys produce different size openings in the instrument. The air columns inside the instrument are then made shorter or longer which produces different sounds.
Our ears serve as a bridge for sound waves to pass. The human ear that attaches to both sides of the head acting as a funnel to catch even the tiniest sound around. The inner ears, eardrums and tiny bones inside the ear, called the hammer, anvil and stirrup all begin to vibrate as the sound waves start to enter the inner ear. Sound vibrations then move through an oval opening, called the cochlea. In the cochlea–a snail shell-like, fluid-filled chamber–the sound waves stimulate tiny hairs that are connected to the auditory nerve or the hearing-nerve. The auditory nerve receives signals from the nerve cells and transmits them to the auditory center in the brain.
The brain receives these messages from the auditory nerve. The messages come in fast and furious, in a jumble of confusion, but the brain has the ability to sort them into an organized pattern. This way we can understand the sounds we hear as music or human speech.
A human beings ear hears an audible sound waves, if their frequency ranges from 20 to 20,000 vibrations/second. Subsonic has a frequency that is less than the audible sound waves. Ultrasonic have a frequency higher than the audible sound waves.
Animals like dogs have a higher frequency of hearing sounds. This capability allows the animals to hear sounds that humans can’t. It is also through this capability why animals can sense oncoming danger.
Therefore, sound serves as a warning and prepares the animals for defense and attacks.
Sound travels at a speed of 767 miles/hour or 1,230 kilometers/hour. Sound travels 4.3 times faster in water than air, having a speed of 1,482 meters/second. Sound travels 3 times faster through steel material, having a speed of 4,512 meters/second. Light travels faster than sound, having a speed of 186,000 miles/second or 299792.458 kilometers/second. You can observe a lightning flash coming first before hearing the sound.
A whale’s voice travels at a maximum speed of 800 kilometers or 479 miles in the water. Dolphins hears sounds from 24 kilometers or 15 miles away underwater.
Sound waves are scientifically studied. It is technically referred to Acoustics.
Sound waves can bend around corners and obstacles.
No sound can travel in a vacuum, which is an area having no air at all.
Wind has no sound. The wind blowing against an obstacle makes a sound.
In space, no sound is produced because of the absence of corners and obstacles, where sound waves are supposed to bounce off.
When sound waves bounced off on objects instead of absorbing the sound waves, you can hear echoes produced. The echo is a reflection of the sound waves produced because of the bouncing off of waves.
If you have bigger object, where the sound waves will bounce off, then more and louder echo is produced.
The loudest sound naturally occurs on Earth is the sound coming from a volcano eruption. The Krakatoa eruption in 1883 was recorded to have the loudest sound produced in the world. The sound was heard at a 4,000-mile distance.
Sound is also considered as an energy. This happens when things vibrates and that vibration travels through the ears. And then, the sounds are recognized. The sound produced during the vibration travels through the matter. When you talk molecules vibrates, producing sound waves that travel to the listener.
·Sound vibrations also travel from one matter to another matter. If you are going to tap the table, sound vibration is produced. When you tap, the sound waves pass through the table and then, it will travel going to the ears.
The absence of matter produces no sound because the sound vibrations do not have a matter to pass through.
Human beings and animals uses sound as a tool or means of communication. There is an Electrocardiogram, Ultrasonic cleaners and Ultrasound for doctors; Sonar for geologists; Doppler for weather services and Echolocation for navigation of animals.
In our daily life, we often use our muscles to pull or push things: we pull up a glass of milk to get it to our mouth; we push an object to move in particular direction etc. We come to realize that either a “pull” or “push” is required to move an object. So, Force is a push or pull on an object.
We use force to walk, to lift any object, to throw anything, to move any object from its place etc. In short, force is there in every activity we do. By applying force we usually bring anything in motion or in rest position but not always. Example: If we apply force on a wall it does not move.
Force has many effects on the objects it is applied to. It can cause many changes to the object to which force is applied.
Force can bring stationary object in motion provided there is no other force preventing the motion. When we apply force on any stationary object, it starts moving in the direction of force. A change in object’s position is called motion.
Example: When we push any toy car, it moves.
So, when force is applied, a stationary object comes in motion or force changes the position of stationary object.
Force changes the motion of body that is already in motion.
Example: When we push harder to moving toy car, its speed increases. Similarly we can apply force in opposite direction of the motion to slow down the speed of the toy car.
Therefore, we can say that force changes the speed of an object.
When we apply more force in the opposite direction of the motion, an object stops moving.
Example: When we try to hold the ball thrown to us with force greater than the force with which it is coming, it stops.
Therefore, we can say that force can also stop a moving object.
When a force is applied at an angle to a moving object, force changes the direction of the moving object.
Example:
When we force is applied on an object its shape and size changes.
Example:
There are many different kinds of force. Some of them are:
We brush our teeth, lift our bag, write with our hand, walk to the school, and get up from our desk. In all these activities we do use our muscles to apply force. The force applied by our muscles to carry out all our activities is called muscular force.
Example:
Force applied by a machine is called mechanical force.
Example:
When we throw a ball up in the sky, it comes down and when we jump, we come back on earth. Why this happens? This is the earth which pulls things towards it. That is why apple drop down on the ground from a tree instead of going into the sky. The pull of the earth is a kind of force. This force is called gravitational force. It is this pull of the earth which keeps us and other object on earth from drifting into space. This force was discovered by Sir. Isaac Newton.
A magnet is a material that attracts things made of iron, nickel and cobalt.
Force of magnet is called magnetic force.
When we roll down a ball on grassy ground, it gradually slows down and finally stops. This happens because a force acts between the ball and the ground. Therefore, frictional force is the force exerted by a surface as an object moves across it or makes an effort to move across it.
Example: When we slide pencil across the surface of a desk, then the desk exerts a friction force in the opposite direction of its motion and pencil slow down and finally stops sliding.
Since friction slow down or prevent motion, it prevents us from slipping all the time, enable us to walk without falling, apply break in our vehicles, makes the movement of vehicle possible on road.
Frictional force is greater on rough surfaces such as grassy ground, on woolen clothes and lesser on smooth and slippery surface.