Y10 Physics

Physics – Kinematics 1

Unit Overview - Motion and Forces

Key and Related Concepts – Brainstorm what you associate with the concepts below.

What is Physics?

Physics - the study of the most fundamental interactions between time, space, energy and matter.

• What is meant by “fundamental”?

• What is meant by “interaction”?

Physics focuses on constructing simple models to describe and explain phenomena.

• What is meant by simple? What is its opposite?

  • Simple – few component parts

  • Complex – many component parts

• What is a model?

  • A model is a representation of something that cannot be directly observed.

The free-body diagram is a simple model that represents the skier on the slope.

This Photo by Unknown Author is licensed under CC BY

This year, we will be studying two important branches of physics called Kinematics and Dynamics that focus on understanding motion and forces.

• The combination of the two branches is called Mechanics:

Kinematics + Dynamics = Mechanics

Motion and Forces

Kinematics and Dynamics

Focus is on describing the PROPERTIES of moving objects.

Focus is on explaining motion and changes in motion using forces.

Key Vocabulary

Predict: see if you can predict the formulas for some of the terms below (with a *)

Kinematics – the branch of Physics concerned with describing the properties of moving objects, without considering causes

motion - the continuous change in position of an object

scalar quantity – a quantity that requires only magnitude (size and appropriate units) to be fully described. Examples: temperature, mass, volume, distance, speed, etc.

vector quantity – a quantity that requires both magnitude and direction to be fully described. Examples: velocity, acceleration, force

“Δ” or “change in” = final state - initial state

rate – ordered comparison of quantities with different units (“ordered” means order of terms in the rate is specific)

rate of change – ordered comparison of how one quantity changes in relation to the change in another quantity with different units

distance ( ) - the length of the path travelled

*speed ( ) – rate of change of distance with time

position ( ) - location and direction from a reference point

*displacement ( ) – change in position

*velocity ( ) – rate of change of position with time

*acceleration ( ) – rate of change of velocity with time

* Based on the definition, can you predict the equation?

We will use the above terminology consistently through this unit. It is recommended that you commit the definitions to memory so you can internalize them.

Introduction to Vectors

Until now, we have been discussing scalar quantities.

scalar - a quantity with magnitude (size and appropriate units), but not

direction.

In the study of motion, sometimes direction must be considered in order to understand

the way objects move:

vector - a quantity that requires both magnitude and direction to be

fully described.

Examples: distance is a scalar quantity

displacement is a vector quantity

Representations of vectors

A letter with an arrow above it, eg. 𝐴𝐴⃑ , is used to represent a vector. A vector may also be

represented graphically.

Algebraic Form Graphic Form

[E]m57=A



The length of the line segment represents

the magnitude of the vector and the tip of

the vector (arrowhead) points in the

direction of the vector.

tip of

vector

tail of

vector

vector

symbol magnitude

(size & units)

direction

Communicating Direction

What is necessary for effectively communicating direction?

A reference point is essential to giving directions properly. A common way to indicate

directions is using compass points:

Motion in 1-D

Motion in one dimension is motion along a straight line. For motion along a straight line,

there are two possible directions.

Examples:

• Moving forward or backward

• Left or right

• Up or down

Positive and negative signs are used to indicate two opposite directions:

Convention

+ −

up down

right left

North South

East West

N

W

S

E

Indicating Direction in 2-Dimensions

Motion in a plane (2-D) requires the use of the compass rose for indicating direction.

The direction of the vector shown above is East [E]. The compass rose can still be used

to indicate direction, even when a vector does not align perfectly with the labelled

directions shown above. Consider the vector shown below:

The direction of the vector is given as [E 20° N] and can be read as “20° North of East”.

In this notation:

• direction on the left is the reference line on the compass rose

• measure in degrees is the angle between the reference line and the vector

• direction on the right is the direction from the reference line toward which the

angle is swept. If North is used as the reference line then the direction of the

vector is [N 70° E]

tip of
the vector (arrowhead) points in the
direction of the vector.
tip of
vector
tail of
vector
vector
symbol magnitude
(size & units)
direction

Communicating Direction
What is necessary for effectively c