Thursday, January 1, 2015

Class 8 Physcis Force and Pressure Key Term to revise before exam

1. A push or a pull acting on an object is called a force

2. Force has magnitude as well as direction.

3. A force between the two objects only when they interact with each other.

4. The sum of forces acting on bodies is called net force.

5. Forces applied on an object in the same direction add to one another then net force = f1 + f2

6. If the two forces act in the opposite directions on an object, the net force acting on it is the difference between the two forces. then net force = f1 +(- f2)

7. Net force on an object is zero if the two forces acting on it in opposite direction are equal

8. A Force can Change the State of Motion

9. If the force applied on the object is in the direction of its motion, the speed of the object increases.

10. If the force is applied in the direction opposite to the direction of motion, then it results in a decrease in the speed of the object

11. The state of motion of an object is described by its speed and the direction of motion

12. Force on an object may change its shape.

13. Force may make an object move from rest.

14. Force may change the speed of an object if it is moving.

15. Force may change the direction of motion of an object.

16. Force may bring about a change in the shape of an object.

17. The force resulting due to the action of muscles is known as the muscular force.

18. Force can be applied only when it is in contact with an object, it is also called a contactforce.

19. The force of friction always acts on all the moving objects and its direction is always opposite to the direction of motion.

20. A force that act without being in contact with two object is called a non-contact force.

21. Muscular and friction forces are type of contact forces.

22. Magnetic Force , electrostatic force and gravitational force are type of non contact forces

23. Force exerted by a charged body on another charged or uncharged body is known as electrostatic force

24. every object in the universe exerts a force on every other object. This force is known as the gravitational force.

25. The force by which the earth attract or pull other object toward itself is called force of gravity

26. The perpendicular force acting on a unit area of a surface is called pressure

27. pressure = force / area

28. The smaller the area, larger the pressure on a surface for the same force. Therefore nails have pointed tip and wider head. Pointed end apply sufficient pressure to push into wooden object.

29. Forces which act perpendicular to the surfaces is called thrust.

30. Bags are provided with broad straps to reduce pressure on shoulder.

31. The cutting and piercing tools always have sharp edges to increase pressure.

32. Porters place on their heads a round piece of cloth, when they have to carry heavy loads By this they increase the area of contact of the load with their head. So, the pressure on their head is reduced and they find it easier to carry the load.

33. Liquid and gases, too, exert pressure on the walls of their container as air and water exerts pressure in all directions

34. The pressure exerted by this air is known as atmospheric pressure.

35. The Envelop of air around the earth is known as the atmosphere.

36. Our body cannot crushed under atmospheric pressure because the pressure inside our bodies is also equal to the atmospheric pressure and cancels the pressure from outside

37. The SI unit of pressure is the pascal (Pa). It is the pressure exerted by a force of 1 N acting over an area of 1 m 2. Thus 1Pa = 1N/m2