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Answer:</h2>
<u>Friction:</u>
When an object slips on a surface, an opposing force acts between the tangent planes which acts in the opposite direction of motion. This opposing force is called Friction. Or in other words, Friction is the opposing force that opposes the motion between two surfaces.
The main component of friction are:
<u>Normal Reaction (R):
</u>
Suppose a block is placed on a table in the above picture, which is in resting state, then two forces are acting on it at that time.
The first is due to its weight mg which is working from its center of gravity towards the vertical bottom.
The second one is superimposed vertically upwards by the table on the block, called the reaction force (P). This force passes through the center of gravity of the block.
Due to P = mg, the box is in equilibrium position on the table.
<u>Coefficient of friction ( </u>μ )<u>:
</u>
The ratio of the force of friction and the reaction force is called the coefficient of friction.
Coefficient of friction, µ = force of friction / reaction force
μ = F / R
The coefficient of friction is volume less and dimensionless.
Its value is between 0 to 1.
<u>Advantage and disadvantage from friction force:
</u>
- The advantage of the force of friction is that due to friction, we can walk on the earth without slipping.
- Brakes in all vehicles are due to the force of friction.
- We can write on the board only because of the force of friction.
- The disadvantage of this force is that due to friction, some parts of energy are lost in the machines and there is wear and tear on the machines.
<u>How to reduce friction:
</u>
- Using lubricants (oil or grease) in machines.
- Friction can be reduced by using ball bearings etc.
- Using a soap solution and powder.
Answer:The correct options are:
1. A system is a group of objects analyzed as one unit.
2. Energy that moves across system boundaries is conserved.
Explanation:
A system is defined as group of interrelated or interacting items existing as a single unit or a whole to achieve a specific objective.Energy lost by the system is equal to the energy gained by the surroundings.
Two statements are true about a system:
- A system is a group of objects analyzed as one unit.
- Energy that moves across system boundaries is conserved.
The main (and only) purpose of the turbine in the turbo jet engine is to drive the air compressor. The turbojet engine works by compressing the air using an inlet and a compressor, then mixing the fuel with the compressed air, then passing the mixture to the combustor, then passing the high pressure air through a turbine and a nozzle.
Kepler's first law - sometimes referred to as the law of ellipses - explains that planets are orbiting the sun in a path described as an ellipse. An ellipse can easily be constructed using a pencil, two tacks, a string, a sheet of paper and a piece of cardboard. Tack the sheet of paper to the cardboard using the two tacks. Then tie the string into a loop and wrap the loop around the two tacks. Take your pencil and pull the string until the pencil and two tacks make a triangle (see diagram at the right). Then begin to trace out a path with the pencil, keeping the string wrapped tightly around the tacks. The resulting shape will be an ellipse. An ellipse is a special curve in which the sum of the distances from every point on the curve to two other points is a constant. The two other points (represented here by the tack locations) are known as the foci of the ellipse. The closer together that these points are, the more closely that the ellipse resembles the shape of a circle. In fact, a circle is the special case of an ellipse in which the two foci are at the same location. Kepler's first law is rather simple - all planets orbit the sun in a path that resembles an ellipse, with the sun being located at one of the foci of that ellipse.
1.commensalism
2. pred-prey
3. parasite-host
4.commensalism