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pressure is a measure of force per unit area. This can be written in equation form as:

P=F/A, where P is pressure, F is force and A is area.

The unit for pressure is N/m2 or Pa (Pascals)

The unit for force is N (Newtons)

The unit for area is m2

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Pressure is a measure of the amount of force applied on a surface, per unit area of that surface

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for a fixed amount of force, if it’s spread out over a large surface area, the force per unit area is small, so the pressure is small. However, for that same force, if it’s concentrated on a small area, the force per unit area is larger, so the pressure is larger

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for a fixed area, if you apply a huge amount of force, you’ll be applying a large pressure on that area. For that same area, if you apply a smaller force, the pressure will be smaller

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friction as the force between two surfaces which impedes motion and result in heating

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friction as the force between two surfaces which impedes motion and result in heating

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The force of friction opposes motion. Think about the direction in which an object is moving. Friction is the force that acts in the opposite direction.

During the movement of the object some energy is wasted as heat produced by the friction of the object with another.

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If you change the air drag to 600N you can find that the resultant force is 0N. We say that the forces on the car are balanced so it will continue to move in a constant speed on a straight line.

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We have a car with the egine that move the car forward with a force of 600 and the air drag push the car in the opposite side with a force of 400N.

Resultant force = 600N - 400N = 200N to the right

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Air resistance is a form of friction caused when an object moves through the air. The air drag produces a force that works in the opposite direction of the movement of the object.

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'limit of proportionality' for an extension-load graph

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'limit of proportionality' for an extension-load graph

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The ‘limit of proportionality’ or ‘elastic limit’ is the point at which a spring stops to follow the Hook’s law and it is permanently damaged. If the load is removed the spring will not return all the way to its original, undeformed length. On the graph, beyond the limit of proportionality the graph is no longer a straight line.

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Hooke’s Law states that within the elastic limit, the extension (x) of an object is directly proportional to the force (f) that causes the extension.

F is directly proportional to x (F ∝ x).
mathematically written, Hooke’s Law is F=kx.

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An experiment that we can do is the extension of a spring under the force of a load.

To study this fenomena we use the extension-load graph.

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We say extension when an object, such as springs or a rubber band, increases their length. And we say compression when it decreases its length

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change of the size, shape and motion of a body 

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change of the size, shape and motion of a body 

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When an external force acts on a body, it may change the direction it moves in, its speed, or cause it to start moving from rest. Sometimes, the force might cause a rearrangement of the molecules making up the body, causing it to change in size or shape .