Science questions in details [4 marks ]

A Contact force as the name suggests acts on a point of an object by direct contact. The Contact may be Continuous or sometimes momentary. The former case is known as Continuous force and the latter case is known as impulse force.
Example: Pushing an object along the floor: This is an example of a continuous force. Here, continuously, the direct force is put on the object to move it along the floor.

Frictional Force refers to the force generated by two surfaces that contacts and slide against each other. These forces are mainly affected by the surface texture and amount of force impelling them together. The angle and position of the object affect the amount of frictional force. If an object is placed flat against an object, then the frictional force will be equal to the weight of the object. If an object is pushed against the surface, then the frictional force will be increased and becomes more than the weight of the object.

Rubber sucker a device used in toys, sunlight blocker - suction cups, suction clamps and various other places where "sticking" is required for temporary period and when you don't want to use glue.
The principle on which Rubber suckers work: When the sucker is pressed against the surface, it squeeze out the air that is behind it. The atmospheric pressure on the outside of the sucker holds its rim firmly against the smooth surface.

A wider strap distributes the force throughout a greater surface area. You can do a comparison using a simple physics equation.
Pressure = Force/Area.
So take two different straps and measure the area of them.
Then find out how much weight the pack will be holding.
Then divide the Weight by the Area and you end up with pressure.

The air molecules at lower altitudes are more compressed by gravity than the ones at the higher altitudes. The pressure level is highest right at the surface of the earth because the air at this level is supporting the weight of all the air above it. More weight above means a greater downward gravitational force. As we move up through levels of the atmosphere, the air has less air mass above it and gravity isn’t strong enough to pull down a greater number of particles. So the balancing pressure decreases. This is why atmospheric pressure drops as we rise in altitude.

If life an object which is moving over a horizontal surface does not continue with constant velocity when the accelerating force is removed. Instead the object slows down and eventually stops. The deceleration is caused by a frictional force between the object and the surface on which it travels. A frictional force always acts to oppose the motion of an object over a surface and is an example of a contact force. When we try to slide one object over another, we find that there is a force which opposes the motion. This force is called friction. Whenever there is relative motion of two surfaces in contact, there is frictional resistance. When a body moves over another, it has to overcome friction. This needs energy. Hence, some energy is always wasted in overcoming friction. When two parts of a machinery rub against each other heat is produced, and the efficiency of the machine decreases. There will be a greater wear and tear in the different parts of a machine due to friction.

Activity: To show tiny bits of paper gets attracted to electric force.
Theory: Electrostatic force is the force exerted by one stationary object having electric charge on other stationary object having electric charge. If the charge on both the objects is same, they will repel and if the charge on both the objects is different then they will attract each other. There are mainly two types of charges positive and negative.
Materials required: tiny bits of paper, plastic ruler/comb
Experiment:
Rub the plastic ruler/ comb with a sheet of paper.
This process will ensure that the ruler/ comb gets charged.
Now immediately bring the ruler/ comb towards the bits of paper.
Conclusion: We will observe that the bits of paper will be attracted towards the ruler/ comb. This happens because the charge acquired by the ruler/ comb exerts a force on the paper and thus attracts it.

All the liquids exert pressure on the base or bottom and walls of their container. All the liquid have weight. When we pour liquid into a vessel, then the weight of liquid pushes down on the base of the vessel producing a pressure. The liquid exerts pressure on the base of the vessel. The pressure exerted by a liquid changes with depth in the liquid. The pressure exerted by a liquid increases with increasing depth inside the liquid. The pressure exerted by a liquid is small just under the surface of the liquid. But as we go we deeper in a liquid the pressure of liquid increases. As the depth of liquid increases the weight of liquid column pushing down from above increases and hence the pressure also increases.