physics study guide

PHYSICS STUDY GUIDE – DR. V PERIOD 10, SEMESTER 1

1. Distance – Length from one point to another; always +.

Displacement - The length of the straight line drawn from its initial position to the object’s final position; can be + or -.Change in position = final – initial position or (∆X = Xf – Xi)

Speed – Measure of the distance over time. Has no direction, only magnitude.Average speed = distance traveled/time of travel.

Velocity – Displacement divided by the time interval. Describes a motion with both a direction and numerical value (magnitude). Average Velocity = (∆X / ∆T) or displacement/time interval.

2. Cannot use the average velocity equation (v=∆x / ∆t) when there is acceleration. You have to use (change in velocity / time required for change).

3. Yes, but only if the final displacement is zero.

4. Constant speed, but the velocity is changing due to its direction.

5. Typical metric units of displacement – meters.

6. Slope of a v-t graph is the acceleration and never curves. The area (under the slope) is the displacement.

7. Slope of a d-t graph is the velocity. Curved line = acceleration. The area (under the slope) is the velocity.

8. Area of an a-t graph is the change in velocity.

9. Horizontal line on a d-t graph means that the displacement is currently 0 (no movement). On a v-t graph – it is a constant velocity. On an a-t graph – there is no acceleration (constant velocity).

10. Negative slope on a d-t graph means that it has a constant negative velocity. On a v-t graph, the acceleration is negative.

11. Beneath the axis on a v-t graph – object is slowing down.

12. Three ways of acceleration: increasing speed, decreasing speed, and changing direction.

13. Turn a corner with constant acceleration? No, because the velocity changes due to direction. Zero acceleration? No, because the speed would also be zero.


14. Negative velocity and positive acceleration? Yes, with free-falling objects. Positive velocity and negative acceleration? Yes, with projectiles.

15. Acceleration of an object in freefall – 9.8 m/s/s. What are some examples? Baseball, football, etc.

16. Acceleration – Zero in horizontal. -9.8 m/s^2 in vertical. At peak, horizontal is 0, vertical is 0. Just before caught, the acceleration is force of gravity.

17. Vertical velocity of ball thrown straight up when it reaches its peak = 0 m/s.

18. Velocity upward – 20 m/s. Speed before caught – 9.8 m/s.

19. Displacement – 0.5(initial velocity+final velocity)(time interval)

20. 0.5(0+9.8)(1) = 1.96 m. Or TNEOMS equation, Dx=(0)(1)+0.5(9.8)(1)^2 =1.96 m.

21. What angle to travel farthest – 45 degrees.

22. Terminal Velocity – When force of drag acting on it is equal to force of gravity acting on it. Occurs during free-fall when acceleration equals zero because of air resistance.

EQUATIONS:

Displacement = ∆X = [Xf – Xi]Velocity = [∆X / ∆T] (∆X is displacement)

With acceleration, use ∆V / time required for change. Speed = [∆D / ∆T] (∆D is distance)Acceleration = [F / M] or [∆V / ∆T]

TNEOMS EQUATIONS (as copied from Dr. V’s website):

Vf = Vi + aDtDx = Vi Dt + ½ a Dt2

Vf2 = Vi

2 + 2aDx

Dx – displacement. Vi – initial velocity.Dt – change in time. Vf – final velocity.A – acceleration (must be constant).


23. Inertia – proportional to the mass. Heavier an object, the more inertia. A body’s mass measures its inertia.

24. The inertia is the same.

25. Yes, natural force.

26. Yes, it still has internal force. (Inertia).

27. Friction – The resistive force that keeps an object from moving.

28. Earth moves in a circle because of its and the sun’s gravitational pulls. Otherwise, it would continue towards the sun.

29. Mass vs. weight = Mass is one’s weight in proportion to its gravitational field. To find mass, you must multiply the weight (in kg) x 9.8 (gravity) to get the mass in kg.

30. Benefit corners – Causes the passenger lean closer to you while making a turn. Newton’s Third Law – a force is exerted on an object when that object interacts with another object in its environment.

31. The penny would drop. To an observer, it would fly backwards.

32. Newton’s Second Law – NF = ma, or net force = mass x acceleration. The acceleration of an object is directly proportional to the net force acting on the object and inversely proportional to the object’s mass.

33. Normal Force – A force that is perpendicular to the surface upon which an object moves. NF = -mg. Also, the weight of an object + any vertical forces on the object. Gravity.

34. Tension in each rope is equal to half of the object’s mass.

35. Direction of friction acts in the opposite direction as the direction of motion.

36. Static Friction – Happens when the force of friction is greater than the applied force; results in no motion.

Kinetic Friction – Happens when the object “breaks free” and moves. The force upon the object overcomes the force of friction.

37. Normal force always equals weight? No. The normal force and weight are the same only when there are no forces acting upon it.


38. Because only one object is moving, the horse. The cart’s velocity = 0 until the horse pulls it.

39. There is a greater force on the fly because the flyswatter has a larger mass, but the fly has the greater acceleration. (Eq = F=ma).

40. Newton’s Third Law – If two objects interact, the magnitude of the force exerted on object 1 by object 2 is equal to the magnitude of the force simultaneously exerted on object 2 by object 1, and these two forces are opposite in direction.

41. Units of force – N, newtons.

EQUATIONS:

Force: F=ma.Newton’s Second Law: Net force = ma.Coefficient of Friction: μk = Fk / FnCoefficient of Static Friction: μs= Fs,max / FnForce of friction: Ff = μFnMoment of Intertia: F= d / dt(mv)

42. Units for momentum – Mos, kg-m/s, m * v

Impulse – final momentum – initial momentum, kg-m/s, f * t,

43. Conservation of Momentum – Total momentum of two objects before a collision is equal to the momentum of the two objects after collision. Momentum lost by object 1 = momentum gained by object 2.

44. Vectors For Momentum:

a. Head on collision (two objects move in opposite directions and collide)


b. Back end collision (two objects moving in same direction and then collide)

c. T-bone (two objects colliding at 90 degrees)

45. Impulse is the measure of the change of momentum.


46. Force is proportional to time, so the more time, the smaller force at the first moment of impact.

47. Following through increases the time in which the collision occurs, making the force smaller. It leaves the bat or racket with more velocity and makes the ball go faster.

48. You’d rather have it break. If it bounces, it’s applying a larger amount of force.

EQUATIONS:

Momentum – P=MV.Impulse – Ft = mvf-mvi.F=ma or Ft=m∆V.

49. Vector – has both magnitude and direction. Ex. Velocity, acceleration, and force.

Scalar – has magnitude but no force. Ex. Time, mass, volume, and speed.

50. Force, velocity, energy and momentum are all vectors.

51. Vectors are added with the head to tail method.

52. Name of vector that connects from start to finish – resultant.

53. Adding east and west vectors; east and north:


55. Equilibrant – Vector that is the same size as the resultant would be, but points in the opposite direction and also touches the other vectors head-to-tail.

56. Breaking a vector into components -

57. Force diagram –Picture representation that is drawn to analyze the forces acting on a free object.


58. The weight shown on the scale is actually the normal force the scale is exerting to support the person’s weight. When the elevator moves upwards, the scale has to push upward to accelerate the person’s mass upward. When the elevator moves down, the normal force decreases.

59. While standing, a person’s center of gravity runs through the middle of their body. Their weight is distributed evenly between both feet. If you lift your leg, your center of gravity shifts to one side and the scale value increases.

60. When solving for a vector - Magnitude and direction are needed.

61. Potential energy – Stored energy; Ability of an object to do work due to its position. Kinetic energy – Energy of an object due to its motion.Energy units – 1 Joule = .239 Calories. 1 Watt = 1 J/s.

62. 3 ways to change the energy of a system – Heat, movement, electricity.

63. Conservation of Energy – Energy can neither be created nor destroyed by itself. It can only be transformed. Friction causes a transformation of energy in the form of heat. Efficiency is the measure of how much energy is used usefully.

64. Mechanical advantage for machines – How much easier and faster a machine makes work. To find the MA, you divide the resistance force by the effort force. Most of the time, the resistance force is the weight of the object (N). Yes.

65. Three types of levers – Pulleys (=1), Wheels and Axels ( >1), Levers (>1).


66. Power – Ability to do or produce effort. Work – the act of doing/producing effort. Power is the ability to do work. Power units – Watt (W) which is equal to 1 J/s, or ergs per second (Erg/s) or Horsepower (Hp).

67. How does PE change when you double the height – The greater the height, the greater the PE. (PE = M * G * H) and is proportional to height, so it will double.

68. KE – Proportional to the square of its speed. So, if the speed doubles, the KE is x by a factor of 4. (KE = ½ * M * v^2)

69. Car speed vs. skidding distance: X2 speed = X4 skidding (stopping) distance.

70. When an object’s height decreases, it’s PE decreases.

71. Potential energy is stored in springs.

72. A machine cannot increase both force and distance, but can multiply your work.

EQUATIONS:

PE = mgh.KE = 0.5m*v^2

73. The velocity and force is constantly changing while moving in a circle, due to the constant change in direction.

74. You may be going the same speed, but if you are constantly changing your direction, your velocity is changing. A = change in velocity / time, so the acceleration changes.

75. “Centripetal” – acting in a direction towards a center or axis. A centripetal force makes a body follow a curved path.


76. When the centripetal force is….

a) Friction –

b) Tension –

Tether = tension.

c) Weight –


EQUATIONS:

Centripetal Velocity = (2piR) / T.Centripetal Acceleration = (v^2) / R.Centripetal Force = m * a = (m * v^2) / R.Tension = (mv^2) / R.

TORQUE:

77. Torque – Easiness of a force to rotate about an axis. You can have a force pushing you forward / backward but not around a central point.

78. Two requirements for total equilibrium – The total torque must be 0 and the angular acceleration must be 0.

79. How to determine whether a torque is positive (CW) or negative (CCW).

Positive – Counterclockwise.

Negative – Clockwise.

80. Center of gravity of an object –

1. Measure the point at which the object is balanced.2. R(center of gravity) = masses * average of their positions / masses

EQUATIONS:

Torque = FD (Force * Distance or length)Force = T / DDistance = T / F

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