Newtonian Mechanics

Question 0

What is inertia

Answer 0

Resistance to motion ob an object. It is directly related to mass.

Question 1

What is newtons first law?

Answer 1

An object at rest tends to stay at rest and an object in motion tends to stay in motion

Question 2

What is newtons second law of motion

Answer 2

F = MA
Force = Mass x acceleration

The unit of force is a newton (N)
The unit of mass is KG
The unit of acceleration is meters over seconds squared m/s^2

Question 3

What is the formula for gravity and how does it relate to mass and weight

Answer 3

Gravity is a force that creates an acceleration of 9.81 m/s²

Weight (measured in newtons N) is the force created by gravity (represented by the constant G) acting on mass (KG).

Hence a mass of 1kg has a weight of 9.81 newtons

Question 4

What is newtons third law?

Answer 4

Every action has an equal an opposite reaction

Question 5

What is the formula for force applied at an angle without friction. E.g a roller-coaster on downward slope.

Answer 5

F x sinθ

Force multiplied by the sine of the angle

Question 6

What is the relationship between velocity, acceleration and time

Answer 6

V = Vo + A x T

V₀ (initial velocity at point zero) + acceleration x time

Velocity is measured in Meters per second.
Time is measured in seconds
Acceleration is measured in meters over seconds squared m/s²

Question 7

What is the formula for position with respect to velocity, acceleration and time

Answer 7

Χ = V₀ +1/2 At²

Position in meters is equal to the initial velocity + (1/2) acceleration multiplied by time squared.

velocity is measured in meters per second (m/s)
Acceleration is measured in meters per second squared (m/s²)
Time is measured in seconds (s)

Question 8

What is the equation for predicting velocity as a function of position and acceleration

Answer 8

V² = V₀² x A x P

Velocity squared = initial velocity squared + 2 x acceleration x position

Question 9

What is the definition of work in physics

Answer 9

Work = force x distance
Only the component of work included in the direction of the movement is included in the calculations.

The unit of work is joules (j)

Note that static resistance to force does not count as work by this definition.

Question 10

What is Kinetic energy

Answer 10

KE = 1/2 M V²

Kinetic energy = 1/2 mass x (velocity squared)

The unit for kinetic energy is joules (j)
Mass is kg
Velocity is m/s

Question 11

What is the work energy theorem

Answer 11

The net kinetic energy = final kinetic energy minus initial kinetic energy = change in kinetic energy

Question 12

Explain gravitational potential energy

Answer 12

Any object above the ground can release its kinetic energy by falling.
The greater the mass of the object and the greater the height above the ground the more potential energy it contains.

PE = GHM

Potential energy = gravity x height x mass
Unit for potential energy is joules (j)

Question 13

Explain potential energy in a spring

Answer 13

Hooks law states that

PE = 1/2 K X²

K is a constant for the stiffness of the individual spring
X is a variable of how far the spring is pushed or pulled from its neutral position
−−

Question 14

Explain the law of conservation of energy

Answer 14

Within a system
mechanic energy = kinetic energy + potential energy

The sum of the two will stay the same although the ratio will change as gravity converts some potential energy to kinetic energy. For example a stationary roller-coaster at the top of the run has 100 joules of potential energy and 0 joules of kinetic energy. Half way down it has 50 of each. At the bottom its has 100 joules of kinetic energy.

Question 15

What is the difference between speed and velocity

Answer 15

Velocity is rate of change of distance in a given direction hence it is a vector quantity. Speed only refers to rate of change in any direction hence it is a scalar quantity.

Hence a body which changes its direction at a constant speed has changed its velocity.

Question 16

What is angular velocity

Answer 16

In a rotating object (e.g a lathe) it is rate of rotation expressed in radians, often in multiples of π radians.
Symbol is omega (ω)

Question 17

What is angular displacement

Answer 17

The number of rotations made by a rotating object expressed in radians or pi radians
Symbol θ

Question 18

What is the definition of a newton

Answer 18

The amount of force needed to accelerate one kg of mass at 1m/s²

Question 19

Explain angular acceleration

Answer 19

Just like linear acceleration angular acceleration is the
change in angular velocity (radians/second)/ change in time
Units: radians per second squared
Usually denoted with greek letter alpha α

Question 20

Explain moment of intertia in a rotating body

Answer 20

Moment of inertia is the rotation equivalent of force = mass×acceleration. If the mass is concentrated further from the axis of a rotating body it will take more force to move it. This is a type of counter leverage.

Given two wheels of equal weight but one has a smaller radius and thicker height. It will be take less force to accelerate the one with the smaller radius because the mass is concentrated closer to the axis.

I = MK²
Inertia = mass x radius of gyration squared

Question 21

What are the laws of dry friction

Answer 21

1: friction always opposes motion
2: friction force is directly proportional to the normal (perpendicular) contact force between surfaces.
3: friction force is dependant on the nature and surface finish of the surfaces in contact.
4: friction force is independent of the area of contact between two surfaces.
5: friction force is independent of the sliding for low speeds.

Question 22

Explain the concept of static friction

Answer 22

When an object is resting on a surface the the surface is pushing up against it (newtons third law). The force pushing back is represented by R(sub)n.

If a horizontal force is applied to the object a friction force will push back against it in the same way until there is enough force to move the object. This is called static equilibrium.

The strength of friction is denoted by variable μ. The friction coefficient has no units and is always expressed as a ratio.

The strength of friction is equal to R(sub)n × μ

Question 23

Explain the distinction between static friction and dynamic friction

Answer 23

It takes less effort to move a given mass with a given friction coefficient from static than it does to maintain movement one it is started. This is because. Hence given surface will have a lower dynamic friction coefficient than static. In practice the static friction coefficient will also be true for low speeds.

Question 24

What are the three types of friction

Answer 24

Dry friction
Fluid friction
Rolling friction

Question 25

What is the term commonly used for deceleration in physics

Answer 25

Retardation

Question 26

Explain angular accleration

Answer 26

Like linear acceleration angular acceleration is calculated by change in time over change in angular speed.
∆ε/∆t

Question 27

What is the relationship between angular velocity and linear velocity. E.g for a wheel moving a conveyor belt or a spoke and bicycle chain.

Answer 27

Linear velocity = angular velocity × length of radius.

Question 28

Explain effective radius of gyration

Answer 28

Effective radius of gyration is like like a centre of gravity of a rotating object except. The mass of a rotating object is distributed but for the purposes of calculating you assume all the weight is concentrated in that radius. The radius of gyration is always smaller that the total radius. It is calculated by
√I/m
The square root of a moment of inertia around a given axis divided by its mass.

Question 29

Explain torque

Answer 29

Torque = M × k² × α
Torque = mass × radius of gyration squared × angular acceleration