# vce physics

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VCE PHYSICS. Unit 3 Topic 1 Motion in 1 & 2 Dimensions. Unit Outline. Unit Outline. To achieve this outcome the student should demonstrate the knowledge and skills to: - PowerPoint PPT PresentationTRANSCRIPT

VCE PHYSICSUnit 3 Topic 1

Motion in 1 & 2 Dimensions

Unit OutlineTo achieve this outcome the student should demonstrate the knowledge and skills to: apply Newtons laws of motion to situations involving two or more forces acting along a straight line and in two dimensions;analyse the uniform circular motion of an object moving in a horizontal plane (FNET = mv2/R) such as a vehicle moving around a circular road; a vehicle moving around a banked track; an object on the end of a string.Apply Newtons 2nd Law to circular motion in a vertical plane; consider forces at the highest and lowest positions only; investigate and analyse the motion of projectiles near the Earths surface including a qualitative description of the effects of air resistance;apply laws of energy and momentum conservation in isolated systems; analyse impulse (momentum transfer) in an isolated system, for collisions between objects moving along a straight line (Ft = mt);apply the concept of work done by a constant forcework done = constant force x distance moved in the direction of the forcework done = area under force distance graphanalyse relative velocity of objects along a straight line and in two dimensions; analyse transformations of energy between: kinetic energy; strain potential energy; gravitational potential energy; and energy dissipated to the environment considered as a combination of heat, sound and deformation of material; kinetic energy i.e. mv2; elastic and inelastic collisions in terms of conservation of kinetic energystrain potential energy i.e. area under force-distance graph including ideal springs obeying Hookes Law kx2gravitational potential energy i.e. mgh or from area under force distance graph and area under field distance graph multiplied by massapply gravitational field and gravitational force concepts g = GM/r2 and F = GM1M2/r2apply the concepts of weight (W = mg), apparent weight (reaction force, N) , weightlessness (W = 0) and apparent weightlessness (N = 0) model satellite motion (artificial, moon, planet) as uniform circular orbital motion (a = v2/r = 42r/T2) identify and apply safe and responsible practices when working with moving objects and equipment in investigations of motion.Unit Outline

Chapter 1Topics covered:The S.I. System.Position.Scalars &Vectors.Vector Addition & Components.

1.0 The S. I. SystemThe system of units used in Physics is the Systeme Internationale dUnits or more simply the S. I. System. The system has two important characteristics;Different units for the same physical quantity are related by factors of 10.(eg. mm; cm; km)The system is based on 7 Fundamental Units, each of which is strictly defined.All other units, so called DERIVED UNITS, are simply combinations of 2 or more of the Fundamental Units.

1.1 PositionThus a number called -15 is 15 units to the left of 0 on the number line.A number called +30 is 30 units to the right of 0.To specify the POSITION of an object, a point of ORIGIN needs to be defined. It is from this point all measurements can be taken.For example on the number line below the point labelled 0 is the origin and all measurements are related to that point.

1.2 Scalars & VectorsBefore proceeding, it is important to define two general classes of quantities.1. SCALAR QUANTITIES:These are COMPLETELY specified by:A MAGNITUDE (ie a NUMBER)and A UNITExamples of Scalar Quantities would be: Temperature (17oC), Age (16 years), Mass (2.5 kg), Distance (150 m).2. VECTOR QUANTITIES:

These are COMPLETELY specified by: A MAGNITUDE (ie. A NUMBER)and A UNITand A DIRECTION

Examples of Vector Quantities would be: Displacement (2.7 km, West), Force (15 N, Downward), Acceleration (1.5 ms-2, S.E.)VECTORS ARE GENERALLY REPRESENTED BY ARROWS:The length of the arrow represents the magnitude of the vector.The orientation of the arrow represents the direction of the vector.

1.3 Vector Addition SINGLE VECTORDIAGRAMA Vector of:Magnitude; 5 units Direction; NE or N45E or 45TVECTOR ADDITIONTwo Forces act at the Centre of Mass of a body. The first of 4N Eastand the second of 3N SouthDirection:Sin = 3/5 = Sin-1 3/5 = 36.90THE RESULTANT FORCE HAS A MAGNITUDE OF 5 N DIRECTED AT E 36.90 SWhich way will the body move ?In a direction, and with a force, that is the sum of the 2 vectors

1.4 Vector SubtractionAn object moving East at 8.0 ms-1changes its velocity to 8.0 ms-1 SouthWhat is the objects change in velocity ?The velocity change (v) is given by vf - vi(- vI ) is a negative vector. It can be converted to a positive one by reversing its direction.Then, by performing a vector addition, the velocity change v can be obtained.

Direction:Tan = 8/8 = 1.0 = Tan-1 1.0 = 450THE CHANGE IN VELOCITY = 11.3 ms-1 AT S 450W

1.5 Vector Components A Jump Jet is launched from a 150 ramp at a velocity of 40 ms-1What are the verticaland horizontal components of its velocity ?V VERTICAL and VHORIZONTAL are the COMPONENTS of the planes velocity. Vertical Component:V VERTICAL = 40 Sin 150 = 10.4 ms-1Horizontal Component:VHORIZONTAL = 40 Cos 150 = 38.6 ms-1

Motion - Revision Questions Question type:Adam is testing a trampoline. The diagrams show Adam at successive stages of his downward motion.Figure C shows Adam at a time when he is travelling DOWNWARDS and SLOWING DOWN.VectorsA: Acc is UPWARD. In order to meet the requirements set - travelling downward BUT slowing down, he must be decelerating ie. Accelerating in a direction opposite to his velocity. Thus acc is upward.Q1: What is the direction of Adams acceleration at the time shown in Figure C ? Explain your answer.

Chapter 2Topics covered:Distance versus Displacement.Speed versus Velocity.Acceleration.Graphical Representations.

2.0 Distance vs DisplacementDistance is a Scalar Quantity having a magnitude and a unit. The S.I. unit for Distance is the metre (m)Distance is best thought of as: How far you have travelled in your journey.Displacement is a Vector Quantity having a magnitude, a unit and a direction. The S.I. unit for Displacement is the metre (m), plus a directionDisplacement is best thought of as: How far from your starting point you are at the end of your journey.Distance and Displacement may or may not be numerically equal, depending on the nature of the journey.

JOURNEY No 1.Distance = DisplacementAt the end of the run:Distance = 100 m.Displacement = +100 mJOURNEY No 2.Distance DisplacementAt the end of the one lap run:Distance = 400 m.Displacement = 0 m

2.1 Speed vs VelocitySpeed is defined as the Time Rate of Change of Distance.Speed is a Scalar Quantity.Mathematically: Speed = Distance/TimeThe S.I. unit for Speed is metres/sec (ms-1)

Velocity is defined as the Time Rate of Change of Displacement.Velocity is a Vector Quantity.Mathematically: Velocity = Displacement/TimeThe S.I. unit for Velocity is metres/sec (ms-1), plus a direction

INSTANTANEOUS vs AVERAGE VELOCITYThe term velocity can be misleading unless a specific label is attached.The label indicates whether the velocity is an Average value calculated over a long period of time OR an Instantaneous value calculated at any instant of time.A simple example illustrates:A journey of 40 km across the suburbs takes 1 hour; VAV = 40/1 = 40 kmh-1 BUT VINST could be anything from 0 kmh-1 (stopped at traffic lights) to VINST = 100 kmh-1 (travelling along the freeway).IN ALL CALCULATIONS AND EQUATIONS USED IN THE COURSE, ASSUME INSTANTANEOUS VALUES ARE REQUIRED UNLESS OTHERWISE STATED.

2.2 Some Common Speeds

2.3 AccelerationAcceleration is defined as the Time Rate of Change of Velocity.Acceleration is a Vector Quantity.Mathematically: Acceleration = Velocity/TimeThe S.I. unit for acceleration is metres/sec/sec (ms-2)Since acceleration is a vector quantity, a body travelling with a constant speed but in a constantly changing direction must be accelerating.So a cyclist travelling around a corner at constant speed is, in fact, accelerating ! (More of this later).ACCELERATING VEHICLEDECELERATING VEHICLEThe velocity and accelerationare in the same directionThe velocity and accelerationare in opposite directions.

2.4 Graphical RepresentationsMuch of the information delivered in this Physics course is presented graphically. Generally, graphs tell a story and you need to develop the ability to read the story the graph is telling.There are two basic families of graphs you should be familiar with:(a) Sketch Graphs, paint a broad brush, general picture of the relationship between the quantities graphed. (b) Numerical Graphs from which exact relationships may be deduced and/or exact values may be calculated.The Story:As time passes, the distance of the object from its starting point does not change. This is the graph a stationary object. The Story:As time passes, the distance of the object from its starting point is increasing in a uniform manner (the slope is constant). This is the graph an object moving at constant speed. The Story:As time passes, the velocity of the object is increasing in a uniform manner (the slope is constant). This is the graph a constantly accelerating objectThe Story:As time passes, the displacement of the object is increasing more quickly (the slope is increasing at a constant rate). This is the graph a constantly accelerating objectSKETCH GRAPHS

Motion - Revision Questions Question type:In a road test, a car was uniformally accelerated from rest over a distance of 400 m in 19 sec. The driver then applied the brakes, stopping in 5.1 sec with constant deceleration.The graphs A to F below should be used to answer the questions below. The horizontal axis represents time

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