PHYSICS 120 - Mechanics

Accuracy

the degree to which a measured value agrees with an accepted reference value for that measurement.

Base quantity

physical quantity chosen by convention and practical considerations such that all other physical quantities can be expressed as algebraic combinations of them.

Base unit

standard for expressing the measurement of a base quantity within a particular system of units; defined by a particular procedure used to measure the corresponding base quantity.

Conversion factor

a ratio that expresses how many of one unit are equal to another unit

Derived quantity

physical quantity defined using algebraic combinations of base quantities

Derived units

units that can be calculated using algebraic combinations of the fundamental units

Dimension

expression of the dependence of a physical quantity on the base quantities as a product of powers of symbols representing the base quantities.

Dimensionally consistent

equation in which every term has the same dimensions and the arguments of any mathematical functions appearing in the equation are dimensionless.

Dimensionless

a quantity with no measurement units or dimension 1 (a pure number).

Discrepancy

the difference between the measured value and a given standard or expected value

Estimation

using prior experience and sound physical reasoning to arrive at a rough idea of a quantity’s value; sometimes called an “order-of magnitude approximation”.

Kilogram (kg)

SI unit for mass

Law

description, using concise language or a mathematical formula, of a generalized pattern in nature supported by scientific evidence and repeated experiments

Metre (m)

SI unit for length

Model

representation of something often too difficult (or impossible) to display directly.

Order of Magnitude

size of a quantity as it relates to a power of 10 (10^n)

Precision

characteristic or property of an object that can be measured or calculated from other measurements

Second (s)

SI unit for time

SI units

International System of Units

Significant figures

used to express the precision of a measuring tool used to measure a value.

Theory

testable explanation for patterns in nature supported by scientific evidence and verified multiple times by various groups of researchers.

Uncertainty

a quantitative measure of how much measured values deviate from one another.

Units

standards used for expressing and comparing measurements.

Antiparallel vectors

two vectors with angles that differ by 180 degrees

Associative

terms can be grouped in any fashion.

Component form of a vector

vector written in terms of its unit vector components (i, j, k)

Cross product

the result of vector multiplication

Displacement

change in position

Dot product

the result of scalar multiplication of two vectors.

Magnitude

the length of a vector.

Orthogonal vectors

two vectors with directions that differ by 90 degrees.

Parallel vectors

two vectors with exactly the same direction angles.

Resultant vector

vector sum or two or more vectors

Scalar

a number

Scalar component

a number that multiplies a unit vector in a vector component

Scalar quantity

a quantity that can be specified with magnitude only - no direction.

Unit vector

vector of magnitude 1 that specifies direction

i

unit vector in x-direction

j

unit vector in y-direction

k

unit vector in z-direction

Vector quantity

a quantity described using both a magnitude and direction

Acceleration due to gravity

acceleration of an object due to gravity

Average acceleration

the rate of change of velocity over time.

Average speed

the total distance travelled over time.

Elapsed time

the difference between beginning and end time.

Free fall

state of movement that results from gravity only

Instantaneous acceleration

acceleration at a specific point in time.

Instantaneous speed

the absolute value of the instantaneous velocity.

Instantaneous velocity

the velocity at a specific point in time

Kinematics

the description of motion through properties of position, time, velocity, and acceleration.

Position

the location of an object at a particular time

Total displacement

the sum of individual displacements over a given time period.

Projectile motion

motion of an object subject only to the acceleration of gravity

Range

the maximum horizontal distance travelled by a projectile.

Time of flight

elapsed time a projectile is in the air.

Trajectory

path of a projectile through the air.

Dynamics

study of how forces affect the motion of objects and systems.

External force

force acting on an object or system originating from outside the object or system.

Force

push or pull on an object with a specific magnitude and direction.

Inertia

the ability of an object to resist changes in its motion.

Net external force

vector sum of all external forces acting on an object or system, causing acceleration.

Newton (N)

SI unit for force

Newton’s first law of motion

body at rest remains at rest or, if in motion, remains in motion at constant velocity unless acted on by a net external force.

Newton’s second law of motion

acceleration of a system is directly proportional to and in the same direction as the net external force acting on the system and is inversely proportional to its mass. F=ma

Newton’s third law of motion

whenever one body exerts a force on a second body, the first body experiences a force that is equal in magnitude and opposite in direction to the force that it exerts.

Normal force

force supporting the weight of an object or load, that is perpendicular to the surface of contact between the load and its support.

Tension force

pulling force that acts along a stretched flexible connector.

Thrust

reaction force that pushes a body forward in response to a backward force.

Weight force

force due to gravity acting on an object with mass.

Friction force

force that opposes relative motion between systems in contact.

Drag force

force that opposes the motion of an object in a fluid.

Kinetic friction

force that opposes the motion of two systems in contact and moving relative to each other.

Static friction

force that opposes the motion of two systems in contact and not moving relative to each other.

Average power

work done in a time interval divided by the time interval.

Kinetic energy

energy of motion.

Net work

work done by all the forces acting on an object

Power

the rate of doing work.

Work

done when a force acts on something that undergoes a displacement.

Work-Kinetic energy theorem

net work on a particle is equal to its change in kinetic energy.

Angular acceleration

rate of change of angular velocity.

Angular position

angle a body has rotated through in a fixed coordinate system.

Angular velocity

rate of change of angular position.

Instantaneous angular acceleration

derivative of angular velocity with respect to time.

Instantaneous angular velocity

derivative of angular position with respect to time.

Lever arm

perpendicular distance from the line that the force vector lies on to a given axis.

Moment of inertia

rotational mass of rigid bodies that relates to the ease with which the angular velocity can be changed.

Parallel axis

axis of rotation that is parallel to an axis about which the moment of inertia of an object is known.

Parallel axis theorem

if the moment of inertia is known for a given axis, it can be found for any axis parallel to it.

Torque

cross product of a force and a lever arm to a given axis

Total linear acceleration

vector sum of the centripetal and tangental acceleration vectors.

Angular momentum

product of moment of inertia and angular velocity

Precession

circular motion of the pole of the axis of a spinning object around another axis due to a torque.

Rolling motion

combination of rotational and translational motion with or without slipping.

Equilibrium

linear and angular acceleration are zero relative to an inertial frame of reference.

Escape velocity

initial velocity an object needs to escape the gravitational pull of another. Velocity of an object with zero total mechanical energy.

Tidal force

difference between the gravitational force at the centre of a body and at any other location on the body. Causes stretching to the body.

Centre of mass

weighted average position of the mass/

Elastic collision

collision that conserves both momentum and kinetic energy.

Inelastic collision

collision that conserves momentum only.

Explosion

single object (pi=0) breaks up into multiple objects. Does not conserve kinetic energy.