MYP PhysicsMotion

Objectives

1.To understand the concept of motion and how it has evolved through time.

2.To understand the vocabulary associated with motion.

3.To discern the difference between a scalar and a vector quantity.

4.To understand how to illustrate motion through the process of graphing data.

Vocabulary of motion

Acceleration Motion

Average Speed Motion diagram

Circular Motion Position

Constant Acceleration Relative Motion

Displacement Scalar

Frame of Reference Speed

Function Time

Graph Vector

Linear Motion Velocity

Motion

What is motion?

It is the action or process of moving or being moved.

Relative motion

Relative motion is the calculation of the motion of an object with regard to some other moving object.

Think of it like sitting in a car on the freeway. If you are driving at 70 mph and another car passes you going 80 mph, it would seem like you are standing still and the other person is moving away from you at 10 mph.

History

Who was the first person to study and try to explain the concept of motion?

Aristotle

Aristotle, born in 384 B.C. in Stagira, in Thrace, at the northern end of the Aegean, near Macedonia

Aristotle method

1. defining the subject matter

2. considering the difficulties involved by reviewing the generally accepted views on the subject, and suggestions of earlier writers

3. presenting his own arguments and solutions.

Aristotle motion

Every modern child has since birth seen cars and planes moving around, and soon finds out that these things are not alive, like people and animals. In contrast, most of the motion seen in fourth century Greece was people, animals and birds, all very much alive. This motion all had a purpose, the animal was moving to someplace it would rather be, for some reason, so the motion was directed by the animal's will. For Aristotle, this motion was therefore fulfilling the "nature" of the animal,

just as its natural growth fulfilled the nature of the animal.

Aristotle motion

To account for motion of things obviously not alive, such as a stone dropped from the hand, he extended the concept of the "nature" of something to inanimate matter. He suggested that the motion of such inanimate objects could be understood by postulating that elements tend to seek their natural place in the order of things, so earth moves downwards most strongly, water flows downwards too, but not so strongly, since a stone will fall through water.

Aristotle motion

In contrast, air moves up (bubbles in water) and fire goes upwards most strongly of all, since it shoots upward through air. This general theory of how elements move has to be elaborated, of course, when applied to real materials, which are mixtures of elements. He would conclude that wood, say, has both earth and air in it, since it does not sink in water.

Aristotle motion

Of course, things also sometimes move because they are pushed. A stone's natural tendency, if left alone and unsupported, is to fall, but we can lift it, or even throw it through the air. Aristotle termed such forced motion "violent" motion as opposed to “natural” motion. The term "violent" here connotes that some external force is applied to the body to cause the motion.

Aristotle motion

Violent motion

Natural motion

Aristotle motion

Even though Aristotle was not exactly correct in his explanation of motion, he started the process of looking at how and why things move.From this, the study of kinematics arrived.

Kinematics

What is kinematics?It is the branch of mechanics concerned with the motion of objects without reference to the forces that cause the motion.The study of how and not why objects move.

Describing motion

We use the following words to describe motion. position reference point frame of reference time velocity (speed with a direction) acceleration displacement (distance)

Position

Position – separation between object and a reference point.

Formula 1 racing positions relative to starting line.

Reference point / frame of reference

Reference point: zero location in a coordinate system or frame of reference.

Frame of reference: coordinate system used to define motion.

Where are you with respect to City High?

Frame of reference: MapReference point: City High

Reference point / frame of reference

Frame of reference: The City of Grand Rapids and the surrounding suburbs.Reference point: City High School.I live about 10miles southeast of City High, therefore the position of my house is 10 miles southwest of City High.

Time

Motion occurs over a period of time (time interval) or at an instant point in time.

Time interval: difference in time between two clock readings.

Time

A nonspatial continuum in which events occur in apparently irreversible succession from the past through the present to the future.

Velocity

Velocity – the ratio of change in position to time interval over which change takes place (with a direction)

•change in position – displacement

• change in position in linear motion with no

backward motion – distance

Speed - the ratio of change in position to time interval over which change takes place (without a direction)

Vector vs. Scalar

Scalar – quantity, like speed, that has only a magnitude, or size.

Vector quantity – quantity, like velocity, having both magnitude (size) and direction.

Speed – 55 mi/hr

Velocity – 55 mi/hr south

Acceleration

Acceleration – change in velocity divided by time interval over which it occurred. (meters / seconds2)

Constant acceleration – is an acceleration that does not change with time. The increase/decrease in velocity stays the same throughout the motion.

Displacement vs. Distance

What is displacement?Displacement: change in position. A vector quantity.How far away you are from where you were.

Drove home from work.

10 miles

Distance

What is distance?Distance: separation between two points. A scalar quantity. How far away something is with respect to something else.

Drove home from work.

13.2 miles

Distance = Displacement

Going from point A to point B is 5 km.

The distance from point A to point B is 5 km.

The displacement from point A to point B is 5 km.

displacement

Distance = Displacement

When is distance equal displacement? Distance equals displacement when we have linear motion where there is no backward motion.

displacement

Distance ≠ displacement (1 dimension)

Your house Friend’s house Your School

5 km

2 km3 km

Going to school

Stop by your friend’s house after schoolHow far are you from home?

Distance ≠ displacement (2 dimension)

40 m

30 m50 m

Your housefriend 1 house

friend 2 house

Linear motion vs. Circular motion

Linear motion – motion in a straight line

(aka. 1 dimensional)

Circular motion – motion with constant radius of curvature caused by acceleration being perpendicular to velocity.

Motion Diagram

We will use three graphs to show motion. These are called motion diagrams

Displacement (distance) vs. time

Velocity (speed) vs. time

Acceleration vs. time.

Displacement vs. Time graphs

Velocity vs. Time graphs

Acceleration