My Science School

Icebergs are huge chunks of ice that break off from the frozen seas at the North and South Poles as the weather becomes warmer. They can be enormous and are all the more dangerous for shipping because nine-tenths of the iceberg is invisible under water. The famous RMS Titanic was sunk by an iceberg in 1912.

Most icebergs in the Northern Hemisphere break off from glaciers in Greenland. Sometimes they drift south with currents into the North Atlantic Ocean. Icebergs also calve from glaciers in Alaska. In the Southern Hemisphere, almost all icebergs calve from the continent of Antarctica.

Some icebergs are small. Berg bits are floating sea ice that stretch no more than 5 meters (16.5 feet) above the ocean. Growlers are even smaller.

Icebergs can also be huge. Some icebergs near Antarctica can be as big as Sicily, the largest island in the Mediterranean Sea. As little as one-eighth of an iceberg is visible above the water. Most of the mass of an iceberg lies below the surface of the water. This is where the phrase "tip of the iceberg" came from, meaning only part of an idea or problem is known.

There are many different kinds of icebergs. Brash ice, for instance, is a collection of floating ice and icebergs no more than 2 meters (6.5 feet) across. A tabular berg is a flat-topped iceberg that usually forms as ice breaks directly off an ice sheet or ice shelf.

The ice below the water is dangerous to ships. The sharp, hidden ice can easily tear a hole in the bottom of a ship. A particularly treacherous part of the North Atlantic has come to be known as Iceberg Alley because of the high number of icebergs that find their way there. Iceberg Alley is located 250 miles east and southeast of Newfoundland, Canada.

In 1912, the Titanic, a large British ocean liner on its way to New York, struck an iceberg and sank in Iceberg Alley. More than 1,500 people drowned. Soon after the Titanic sank, an International Ice Patrol was established to track icebergs and warn ships. That patrol continues today.

Picture Credit : Google

The minerals dissolved in sea water, which make it taste salty, lower the temperature at which the water will freeze. But at the temperatures found at the far north and south of the globe, the sea is frozen all the time. Further from the Poles, it may also freeze in winter. In fact, the North Pole is permanently frozen sea — there is no land beneath the ice.

Ocean water freezes just like freshwater, but at lower temperatures. Fresh water freezes at 32 degrees Fahrenheit but seawater freezes at about 28.4 degrees Fahrenheit, because of the salt in it. When seawater freezes, however, the ice contains very little salt because only the water part freezes. It can be melted down to use as drinking water. At least 15 percent of the ocean is covered by sea ice some part of the year. On average, sea ice covers almost about 10 million square miles of the Earth.

Sea water becomes more and more dense as it becomes colder, right down to its freezing point. Fresh water, on the other hand, is most dense while still at 39.2 degrees Fahrenheit, well above the freezing point. The average temperature of all ocean water is about 38.3 degrees Fahrenheit.

If the temperature is cold enough, ocean water does freeze. The polar ice cap at earth's North Pole is a giant slab of frozen ocean water. At earth's South Pole, the land mass constituting Antarctica complicates the situation, so most of the ice there is compacted snow. Over cold regions such as Antarctica, Greenland, and Canada, the fresh water in the air freezes to snow and falls onto the land without a melting season to get rid of it. Over time, this snow builds up and compacts into an ice mass known as a glacier. Gravity slowly pulls the glacier downhill until it reaches out onto the ocean, forming an ice shelf. The ocean-bound edge of the ice shelf slowly crumbles into icebergs which float off on their own path. For this reason, glaciers, ice shelves, and icebergs are all thick sheets of frozen fresh water and not frozen ocean water. In contrast, when ocean water freezes, it forms a thin flat layer known as sea ice or pack ice. Sea ice has long been the enemy of ships seeking an open route through cold waters, but modern ice breaker ships have no problem breaking a path through the fields of frozen ocean.

Picture Credit : Google

A refrigerator is basically a box that is very cold inside. The heat inside the box is made to move outside, where it flows out into the air. This is achieved by means of a pipe that contains a fluid called a refrigerant. The refrigerant flows around the pipe, becoming a vapour and then condensing back into a liquid. As it becomes a vapour, the refrigerant takes heat from inside the refrigerator.

The refrigerant, which is now in a liquid state, passes through the expansion valve and turns into a cool gas due to the sudden drop in pressure. As the cool refrigerant gas flows through the chiller cabinet, it absorbs the heat from the food items inside the fridge. The refrigerant, which is now a gas, flows into the compressor, which sucks it inside and compresses the molecules together to make it into a hot, high-pressure gas.

Now, this gas transports to the condenser coils (thin radiator pipes) located at the back of the fridge, where the coils help dissipate its heat so that it becomes cool enough to condense and convert back into its liquid phase. Because the heat collected from the food items is given off to the surroundings via the condenser, it feels hot to the touch.

After the condenser, the liquid refrigerant travels back to the expansion valve, where it experiences a pressure drop and once again becomes a cool gas. It then absorbs heat from the contents of the fridge and the whole cycle repeats itself.

Parts of a refrigerator

A refrigerator consists of a few key components that play a vital role in the refrigeration process:

Expansion valve

Also referred to as the flow control device, an expansion valve controls the flow of the liquid refrigerant (also known as ‘coolant’) into the evaporator. It’s actually a very small device that is sensitive to temperature changes of the refrigerant.

Compressor

The compressor consists of a motor that ‘sucks in’ the refrigerant from the evaporator and compresses it in a cylinder to make a hot, high-pressure gas.

Evaporator

This is the part that actually cools the stuff kept inside a refrigerator. It consists of finned tubes (made of metals with high thermal conductivity to maximize heat transfer) that absorb heat blown through a coil by a fan. The evaporator absorbs heat from the stuff kept inside, and as a result of this heat, the liquid refrigerant turns into vapor.

Condenser

The condenser consists of a coiled set of tubes with external fins and is located at the rear of the refrigerator. It helps in the liquefaction of the gaseous refrigerant by absorbing its heat and subsequently expelling it to the surroundings. As the heat of the refrigerant is removed, its temperature drops to condensation temperature, and it changes its state from vapor to liquid.

All moving objects have momentum. It is their tendency to keep moving unless a force acts upon them. Momentum is calculated by multiplying the mass of an object by its velocity. The greater its mass, the greater its momentum. That means that a train travelling at 25km/h (15mph) along a straight track has a greater momentum than a bird flying at the same speed above it. A much greater force will be needed to stop the train than to stop the bird.

Momentum is the quantity of motion of a moving body. In a basic sense, the more momentum a moving object has, the harder it is to stop. This is why you see the term used metaphorically like in the example of the sports team. It means the team is on a roll (generally, a winning streak) and is becoming a stronger team for it. The other teams will have a harder time stopping the team gaining momentum.

We know that momentum is the quantity of motion of a moving body, but what, exactly, does that mean? Let's think about a baseball being thrown in a straight line through the air in order to try and understand this. When you catch a baseball, you feel the momentum of the ball being imparted to you. The ball will probably push your hand back towards you when you catch it. The more momentum the ball has, the more it will push back your hand as it transfers its momentum to you.

Imagine two baseballs are being thrown at you. One is traveling at 50 mph and the other at 150 mph. Even if you somehow catch that 150 mph ball, it might knock you off your feet. It will take more effort on your part to stop the 150 mph ball than the 50 mph one. So it stands to reason that velocity is a very important aspect of momentum. However, that's not all there is to momentum.

Now imagine two balls being thrown at you at 50 mph. One is a baseball and the other is a bowling ball. You probably aren't going to want to try to stop the bowling ball. It's going to keep traveling even after it hits you. Both balls are traveling at the same velocity, so what makes the bowling ball so much harder to stop? It's because it is heavier. It has more mass. So the other important aspect of momentum is mass.

Involuntary reactions, which happen without conscious thought, such as blinking an eye when an object approaches it, happen in fractions of a second. You can make a comparison of the speed of your conscious reactions and those of a friend by asking him or her to hold a ruler upright from the bottom. Put your fingers around the ruler without touching it. As your friend shouts “Go!” and drops the ruler, close your fingers as quickly as you can. Use the ruler’s scale to compare measurements with friends.

Think fast! Have you ever noticed that when someone unexpectedly tosses a softball at you, you need a little time before you can move to catch it (or duck)? That's because when your eyes see an incoming signal such as a softball, your brain needs to first process what's happening—and then you can take action. In this activity, you can measure just how long it takes for you to react, and compare reaction times with your friends and family.

You may not realize it, but when your senses pick up clues from the outside world—the smell of baking cookies, the color of a stoplight, the rrring! of an alarm clock—it takes a fraction of a second for you to recognize that signal and respond. During that time your brain receives information from your senses, identifies a possible source, and allows you to take action. The jam-packed fraction of a second is called your reaction time.

This activity teaches you about your brain's reaction time, but it also relies on the laws of physics. Specifically, you can calculate your reaction time using our handy chart, which is based on how quickly a ruler falls. How do we know how quickly your ruler will fall? Gravity pulls all objects toward Earth's center at the same speed. If you want to try this out at home, try dropping a tennis ball and a basketball from the same height: They should both hit the ground at the same time!

In the seventeenth century, Sir Isaac Newton developed three laws of motion.

            The First Law of Motion states, "A body at rest will remain at rest, and a body in motion will remain in motion unless it is acted upon by an external force." This simply means that things cannot start, stop, or change direction all by themselves. It takes some force acting on them from the outside to cause such a change. This property of massive bodies to resist changes in their state of motion is sometimes called inertia. 

The Second Law of Motion describes what happens to a massive body when it is acted upon by an external force. It states, "The force acting on an object is equal to the mass of that object times its acceleration." This is written in mathematical form as F = ma, where F is force, m is mass, and a is acceleration. The bold letters indicate that force and acceleration are vector quantities, which means they have both magnitude and direction. The force can be a single force, or it can be the vector sum of more than one force, which is the net force after all the forces are combined. 

When a constant force acts on a massive body, it causes it to accelerate, i.e., to change its velocity, at a constant rate. In the simplest case, a force applied to an object at rest causes it to accelerate in the direction of the force. However, if the object is already in motion, or if this situation is viewed from a moving reference frame, that body might appear to speed up, slow down, or change direction depending on the direction of the force and the directions that the object and reference frame are moving relative to each other. 

The Third Law of Motion states, "For every action, there is an equal and opposite reaction." This law describes what happens to a body when it exerts a force on another body. Forces always occur in pairs, so when one body pushes against another, the second body pushes back just as hard. For example, when you push a cart, the cart pushes back against you; when you pull on a rope, the rope pulls back against you; when gravity pulls you down against the ground, the ground pushes up against your feet; and when a rocket ignites its fuel behind it, the expanding exhaust gas pushes on the rocket causing it to accelerate. 

If one object is much, much more massive than the other, particularly in the case of the first object being anchored to the Earth, virtually all of the acceleration is imparted to the second object, and the acceleration of the first object can be safely ignored. For instance, if you were to throw a baseball to the west, you would not have to consider that you actually caused the rotation of the Earth to speed up ever so slightly while the ball was in the air. However, if you were standing on roller skates, and you threw a bowling ball forward, you would start moving backward at a noticeable speed.