Physics Force and Friction - PDF Material for SSC & RRB Exams
1. A 50-kg object is accelerating to the right at 10 m/s2. What is the magnitude of the rightward net force acting on it (in Newtons)? – 500kgm/s2 (f=ma)
2. Force could be a – push or a pull.
3. A force arises due to- the interaction between two objects.
4. Force has magnitude as well as direction.
5. A change in the speed of an object or the direction of its motion or both implies – a change in its state of motion.
6. Force acting on an object may cause a change in its state of motion or a change in its shape.
7. Force per unit area is called – pressure.
8. Liquids and gases exert pressure on the walls of their containers.
9. The pressure exerted by air around us is known as atmospheric pressure.
10. Friction opposes the relative motion between two surfaces in contact. It acts on both the surfaces.
11. Friction depends on the nature of the surfaces in contact.
12. Static friction comes into play when we try to move an object at rest.
13. Sliding friction comes into play when an object is sliding over one another.
14. Sliding friction is smaller than static friction (static friction > kinetic friction > rolling friction)
15. Friction is important for many of our activities. (without friction we can’t walk)
16. Friction can be increased by making a surface rough.
17. The sole of the shoes and the tyres of the vehicles are treading to increase friction.
18. Friction is something undesirable.
19. Friction can be reduced by using lubricants, polishing, proper selection of material.
20. When one body rolls over another body, rolling friction is smaller than sliding friction.
21. In many machines, friction is reduced by using ball bearings.
22. Fluid friction can be minimised by giving suitable shapes to bodies moving in fluids.
23. The force applied to a cable or wire that is anchored on opposite ends to opposing walls or other objects. This causes a force that pulls equally in both directions- Tension force
24. The spring force is the force created by a compressed or stretched spring.
25. An object travels equal distances in equal intervals of time, then it is said to be in uniform motion.
26. If velocity decreases with time, then its acceleration is negative called deceleration or retardation.
27. Acceleration is a vector quantity and its SI unit is ms-2
28. Graphical representation of motion, Displacement and time graph- Uniform velocity (straight line)
29. In upward direction, velocity of body is decreasing instead of increasing, then equation of motion – 1) V=U-GT, 2) S=UT-, 3). =-2GS
30. If anybody is falling freely under gravity, then acceleration is – Positive acceleration due to gravitational force (g)
31. If an object is thrown vertically upward, then acceleration is – negative acceleration due to gravitational force (-g)
32. For a body with zero acceleration or constant speed, graph between velocity and time will be a straight line parallel to time axis.
33. For accelerating or decelerating body the graph will be a straight line inclined to time axis and velocity axis
34. Graph between position (distance)-time for an accelerating or decelerating body is always a parabola.
35. Acceleration-time graph for uniformly accelerating body is a line parallel to time axis.
36. In case of uniformly accelerated motion, the graph between velocity and time is always a straight line.
37. The motion of a bullet shot from the gun, the motion of a rocket after burning out, the motion of a bomb dropped from an aeroplane are Projectile Motion.
38. If we drop a ball from a height and at the same time thrown another ball in a horizontal direction, then both the balls would strike the earth simultaneously at different places.
39. Circular motion with a constant speed is called uniform circular motion.
40. During circular motion an acceleration acts on the body towards the centre, called centripetal acceleration.
41. The direction of centripetal acceleration is always towards the centre of the circular path
42. SI unit force is newton (N) and CGS unit is dyne. (1 N = dyne. )
43. During circular motion a force always acts on the body towards the centre of the circular path, called centripetal force. (centripetal force = m)
44. In circular motion we experience that a force is acting on us in opposite to the direction of centripetal force called centrifugal force.
45. centrifugal force is an apparent force or imaginary force and called a pseudo force.
46. Cyclist inclined itself from vertical to obtain required centripetal force
47. For taking turn on a curved road, the frictional forces acting between the tyres of the vehicle and the road acts as centripetal force.
48. If a bucket containing water is revolved fast in a vertical plane, the water may not fall even when bucket is completely inverted because a centrifugal force
49. For orbital motion of electrons around the nucleus electrostatic force of attraction is acting between the electrons and the nucleus as centripetal force.
50. Cream is separated from milk when it is rotated in a vessel about the same axis-a centrifugal force
51. For revolution of the earth around the sun, gravitational force of attraction between the earth and the sun acts as centripetal force.
52. A body continues in its state of rest or of uniform motion in a straight line unless an external force act on it. It is based on law of inertia or law of Galileo.
53. When a bus or train at rest starts, to move suddenly, the passengers sitting in it jerk in backward direction due to their inertia of rest.
54. The dust particles come out from a carpet when it is beaten with a stick due to their inertia of rest.
55. A passenger jumping out from a rapidly moving bus or train is advised to jump in forward direction and run forward for a short mile due to inertia of rest.
56. When a running bus or train stops suddenly, the passengers sitting in it jerk in forward direction due to inertia of motion
57. In Projectile motion, Maximum range θ = 45° and maximum height θ=90°
58. SI unit of impulse N-s (or) Kg m/s
59. Newton’s second law of motion- Force =Mass x Acceleration (unit-N)
60. On firing the bullet, the gunner is pushed in backward direction because of Newton’s third law
61. A cricketer moves his hands backwards while catching a ball because of Impulse
62. A person jumping from a height on a concrete floor receives more injury than when jumping on a spongy floor because of Impulse.
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