Unit 2 Physics Area of Study 1 Motion

Area of Study 1 Ch 4 Aspects of Motion Chapter 4 Aspects of Motion

On completion of this chapter,  You will have covered  Terms that describe motion  A graphical description of Motion  Instantaneous and average velocities  Motion with constant acceleration described using graphs and equations of motion  Vertical motion under gravity Area of Study 1 Ch 4 Aspects of Motion

On completion of this chapter,  You will have covered  Terms that describe motion  A graphical description of Motion  Instantaneous and average velocities  Motion with constant acceleration described using graphs and equations of motion  Vertical motion under gravity Area of Study 1 Ch 4.1 Describing Motion in a straight line

Describing Motion  Motion is a fundamental part of everyday life.  Mix:  Competition!! Highest score will win a chocolate bar! Submit your score to win to (keep a screenshot please) Area of Study 1 Ch 4.1 Describing Motion in a straight line

Describing Motion  How do you describe the motion of the flies? (besides frustrating) Area of Study 1 Ch 4.1 Describing Motion in a straight line Position DistanceDisplacement Direction SpeedVelocity How fast they take-offAcceleration

Describing Motion  Throughout this Chapter we will only study “straight line motion ”  Eg.  Trams (along a straight track)  Swimmer in a pool Area of Study 1 Ch 4.1 Describing Motion in a straight line

Centre of Mass  When we analyse the motion of an object, we can simplify any object to a single point – the centre of mass.  We can also refer to this as the balance point of an object.  Figure 4.1 shows the centre of mass of some everyday objects. Area of Study 1 Ch 4.1 Describing Motion in a straight line

Centre of Mass  Demonstration: Baton Throwing.  We can simplify the motion of a complex object to a single point. Area of Study 1 Ch 4.1 Describing Motion in a straight line

Centre of Mass  Figure 4.1 shows the centre of mass of some everyday objects. Area of Study 1 Ch 4.1 Describing Motion in a straight line

Position and Distance Travelled  The position of an object is described from an initial position – the origin.  We can then describe the position of an object as being a particular distance and direction from the origin.  When moving in straight line, the direction can only be positive or negative from the origin.  Or  left or right, up or down, above or below  You must determine the origin and the direction at the start of the problem. Area of Study 1 Ch 4.1 Describing Motion in a straight line

Position and Distance Travelled  The distance travelled is a measure of the actual distance covered during the motion.  It does not matter whether this is positive or negative motion. Area of Study 1 Ch 4.1 Describing Motion in a straight line

Distance Travelled  The distance travelled is a measure of the actual distance covered during the motion.  Distance travelled is measured in metres (m).  It does not matter whether this is positive or negative motion. Area of Study 1 Ch 4.1 Describing Motion in a straight line

Displacement  Displacement is a term that relates more to the position of the object than the distance it has covered.  Displacement is defined as the change in position of an object.  Displacement is represented by an x  x = final position – initial position.  It is possible to travel a long distance but still have zero displacement! Area of Study 1 Ch 4.1 Describing Motion in a straight line

Scalars and Vectors  Physical quantities that only need a number (magnitude) to fully describe them are known as scalars.  Physical quantities that require a number (magnitude) and a direction to fully describe them are called vectors.  Vectors are represented in bold italic type; for example, x, v, a. see Appendix A.  Vectors can be represented by an arrow.  The length represents the magnitude  The angle it is pointing (tail to tip) represents the direction Area of Study 1 Ch 4.1 Describing Motion in a straight line

Scalars and Vectors Area of Study 1 Ch 4.1 Describing Motion in a straight line Scalar QuantitiesVector Quantities MassDisplacement TemperatureVelocity SpeedAcceleration TimeForce Frequency

Adding Vectors  The addition of two vectors is performed by placing the tail of the second vector at the tip of the first.  The sum of the vectors is given by drawing a vector from the tail of the first to tip of the second  10m to the right + 50m to the right = 60m to the right Area of Study 1 Ch 4.1 Describing Motion in a straight line

Adding Vectors  Example 2 (different directions) 50m to the right + 100m to the left = 50m to the left Area of Study 1 Ch 4.1 Describing Motion in a straight line

Subtracting Vectors  We can subtract vectors by adding the negative of the second vector. 50m to the right - 100m to the left = ?  50m to the right m to the left = ?  50m to the right + 100m to the right= 150m to the right Area of Study 1 Ch 4.1 Describing Motion in a straight line

Speed and Velocity  Speed and velocity are both quantities that give an indication of how fast an object is moving.  It is easier to think of it as a change in position over time. The greater the change in position over a given time period, the faster an object is moving.  Speed is a scalar quantity  Velocity is a vector quantity  In physics the SI unit (International Standard) is metres per second – ms -1 (in Year 10 it would have been m/s) Area of Study 1 Ch 4.1 Describing Motion in a straight line

Speed and Velocity  Kilometres per hour (km h -1 ) is often used to describe how fast an object (eg a car) is travelling.  It is useful to be able to convert from m s -1 to km h -1 (Physics File page 115) Area of Study 1 Ch 4.1 Describing Motion in a straight line

Instantaneous Speed and Velocity  Instantaneous speed and velocity is a measure of how fast something is travelling at a particular moment in time. eg. Speedometer  (Figure 4.7 Graph we will look at later) Area of Study 1 Ch 4.1 Describing Motion in a straight line

Average Speed and Velocity  Is a measure of how fast something is travelling over a period of time (interval). Area of Study 1 Ch 4.1 Describing Motion in a straight line

Acceleration  Acceleration is a measure of how quickly velocity changes.  It is better to use the definition that it is the change in velocity over time.  The SI unit for Acceleration is ms -2. (v/t -> ms -1 /s -> ms -2 ) Area of Study 1 Ch 4.1 Describing Motion in a straight line

Change in Velocity  When finding the change in any physical quantity, the initial value is taken away from the final value.  When calculating acceleration, a change in velocity is the final velocity minus the initial velocity: ∆v = v − u  In algebra, a subtraction is equivalent to the addition of a negative term, e.g. x − y = x + (−y). The same rationale can be used when subtracting vectors. Vector subtraction is performed by adding the opposite of the subtracted vector:  ∆v = v − u = v + (−u) Area of Study 1 Ch 4.1 Describing Motion in a straight line