Gce o Level Physics Matter

GCE O LEVEL PHYSICS MATTER

©PIN 2010

Chapter1  Prefix: kilo- 103, deci- 10-1, centi- 10-2, milli- 10-3 etc.  Place your eye directly above the markings to avoid PARALLAX ERRORS.  Precision of metre rule is 0.1cm or 1mm.  Precision of vernier calipers is 0.01cm. (refer pg 10)  Precision of micrometer screw gauge is 0.01mm. (refer pg 11)  Each complete to-and-fro motion is one oscillation. The period of the simple pendulum is the time taken for one complete oscillation.  Most stopwatches can measure time to a precision of 0.1s. Digital stopwatches usually show readings up to two dp. Chapter2  The distance moved per unit time is known as speed. (Speed=distance moved/time taken)  V=d/t where v= speed (m/s); d=distance moved (m) t=time taken (s)  Average speed=total distance travelled/total time taken  Velocity is the change in distance in a specified direction per unit time.  Distance in a specified direction is known as displacement. Velocity can also be defined ad the change in displacement per unit time.  Acceleration=change in velocity / time taken  a=△v / △t OR a = v-u / △t  Acceleration due to free fall (due to gravity) does not depend on the material, size or shape. It is a constant, and is given a special symbol g.  Gradient of distance-time graph is SPEED.  Gradient of speed-time graph is ACCELERATION.  Area under speed-time graph gives DISTANCE MOVED. ** refer pg 34, 35. Deduction of Objects falling without air resistance (FYInfo) 1. Both the feather and the hammer increase their speed at a rate of 10m/s every second, that is, they undergo constant acceleration of 10m/s. 2. The direction of the motion is downward (i.e. towards the centre of the earth). 3. The acceleration does not depend on the masses or the weights of the falling objects. In other words, all free-falling objects (big or small) increase their speed at the same rate. Air resistance is a frictional force. Characteristics: 1. It always opposes the motion of moving objects; 2. It increases with the speed of the object; 3. It increases with the surface area (or size) of the object; 4. It increases with the density of air.

01 Chapter3  Force: push or pull that one object exerts on another. It produces or tends to produce motion, and stops or tends to stop motion.  SI unit of force is newton (N).  Scalars (magnitude only) and vectors (both magnitude and direction) quantities.  Addition of non-parallel vectors using parallelogram / tip-to-tail method (Important: pg 50, 51)  A force can cause: (a) a stationary object to start moving (b)a moving object to increase speed (acceleration) (c) a moving object to decrease speed (deceleration) (d)a moving object to change its direction of motion ** For an object with zero acceleration, the different forces acting on it are balanced or add up to zero- i.e. the resultant or net force is zero. Newton’s first law of motion Every object will continue in its state of rest or uniform motion in a straight line unless a resultant force acts on it to change its state. 

If the resultant force acting on an object is not zero, we say the forces are unbalanced.

Newton’s second law of motion When a resultant force acts on an object of constant mass, the object will accelerate and move in the direction of the resultant force. The product of the mass and acceleration of the object is equal to the resultant force. F=ma where F =resultant force in N m=mass of object in kg a = acceleration of object I ms-2 This equation tells us that: 1. A resultant force F on an object will produce an acceleration a; 2. Doubling the resultant force F on an object will double the acceleration a; 3. With the same resultant force F, doubling the mass m will halve the acceleration a. The SI unit of force is Newton N. One Newton (1N) is defined as the force that will produce an acceleration of 1ms-2 on a mass of 1kg. Newton’s third law (optional) For every action, there is an equal and opposite reaction, and these forces act on mutually opposite bodies. This tells us four characteristics of forces: 1. Forces always occur in pairs. Each pair is made of an action force and a reaction force. 2. Action and reaction forces are equal in magnitude. 3. Action and reaction forces act in opposite directions 4. Action and reaction forces act on different bodies. How does friction affect motion + effects of friction (pg59, 60, 61, 62 free body

diagram) **Friction always opposes motion between two surfaces in contact. 02 Chapter 4  Mass is a measure of the amount of matter or substance in a body.  Mass cannot be changed by its location, shape and speed. (Kg)  Usually measured by a beam balance or calibrated electronic balance.  Weight is a force and has direction. The direction is downwards (towards the center of the earth).  The force is also called gravitational force which is measured in newton (N).  Usually measured by a spring balance or compression balance.  The region surrounding the Earth where gravity is experienced is called the gravitational field.  Gravitational field strength, g is defined as the gravitational force acting per unit mass on an object.  W=mg where W=weight (N) m=mass of object (Kg) g=gravitational field strength (N/kg)  Inertia of an object refers to the reluctance of the object to change its state of test or motion.  The inertia of an object depends on its mass. An object with more mass has greater inertia  The density of a substance is defined as its mass per unit volume (kg m-3).  Pure substances are fixed properties — fixed density.  ρ=m/v where ρ = density m= mass of object (kg) v = volume of object (m3)  Example in pg76  1 g cm-3 = 1000 kg m-3 (working in pg79) Chapter 5  The moment of a force (or torque) is the PRODUCT of the force and the perpendicular distance from the pivot to the line of action of the force.  SI unit of the moment of a force is newton metre (Nm)  Moment of force= F × d where F = force (N) d = perpendicular distance from pivot (m) The moment of a force is a vector. It has both a magnitude and direction. Thus, to completely describe the moment of a force, we need to state its: 1. magnitude in Nm 2. direction as clockwise or anticlockwise.  Principle of Moments: When a body is in equilibrium, the sum of clockwise moments about a pivot is equal to the sum of anticlockwise moments about the same pivot. (Important)  Conditions for equilibrium: When an object is not turning, the clockwise and anticlockwise moments acting on it are balanced. That is resultant moment is zero. Thus, an object in equilibrium must satisfy both conditions as follows:

1. All forces acting on it are balanced, that is resultant force is zero. 2. The resultant moment about the picot is zero, that is the Principle of Moments must apply.  Center of gravity of an object is defined as the point through which its whole weight appears to act for any orientation of the object. (depends on distribution of its mass, refer pg 91)  Stability refers to the ability of an object to return to its original position after it has been tilted slightly. 03 Three cases of equilibrium (pg94): ●

Stable equilibrium because if cone is tilted slightly, it returns to its original position w/o toppling. 1.its centre of gravity rises and then falls back again, 2.the line of action of its weight W about the point of contact C causes the cone to return to its original position. 3.the anticlockwise moment of its weight W about the point of contact C causes the cone to return to its original position.

● The cone is in unstable equilibrium because if it is tilted slightly, it topples over. 1. its centre of gravity falls and continues to fall further, 2. the line of action of its weight W lies outside the base area of the cone 3. the clockwise moment of its weight W about the point of contact C causes toppling. ● The cone is in neutral equilibrium because if it is slightly displaced or rolled, it will stay in its new position. 1. its CG neither rises nor falls; it remains at the same level above the surface supporting it. 2. the lines of action of the two forces W and R always coincide 3. there is no moment provided by its weight W about the point of contact C to turn the paper cone. Conclusion: To increase the stability of an object, we should ensure that: 1. its centre of gravity is as low as possible. 2. the area of its base is as wide as possible. Chapter 6  Energy is the capacity to do work. SI unit: joule (J)  The most obvious form of energy is in movement——moving objects have kinetic energy.  Energy that is stored is known as potential energy. Potential energy can be converted to kinetic energy and vice versa.  Potential energy exists in many forms such as chemical potential, elastic potential and gravitational potential energy which required a reference point. (Important: pg104) Principle of conservation of energy (Important)  Energy can neither be created nor destroyed in any process. It can be converted

from one form to another or transferred from one body to another, but the total amount remains constant. ** Principle of conservation of energy, the ideal pendulum and the non-ideal pendulum (pg106-107)  From the Principle of Conservation of Energy, the total energy output by a machine must be equal to its energy input. However, the energy output is always less than the energy input, as energy is dissipated in the process. (The dissipated energy is usually due to friction. This energy usually takes the form of thermal and sound energy. The energy that is lost to the surroundings is considered wasted energy output. ) Energy input = useful energy output + wasted energy output Efficiency= (useful energy output÷ energy input) ×100% 04  Work done by a constant force on an object is given by the PRODUCT of the force and distance moved by the object in the direction of the force.  W=F×s where W= work done by a constant force F (J) F = constant force (N) S = distance moved by the object in the direction of the force (m)  One joule is defined as: the work done by a force of one newton which moves an object through a distance of one metre in the direction of the force. (1 J = 1 Nm) ** No work is done when: (pg 110) 1.The direction of the applied force and the direction in which the object moves are perpendicular to each other. 2.The force is applied on the object (such as the wall or the pile of books) but the object does not move.  When a body of mass m moves at a speed v, its kinetic energy is defined as: E k= ½ mv2 where E k= kinetic energy (J) m= mass of the body (Kg) v = speed of the body (m/s)  G.P.E. of a body near the surface of the Earth is defined as the product of its weight mg and its height h above the ground. Ep = mgh Where Ep = gravitational potential energy (J) m = mass (Kg) g = gravitational field strength ( N/kg) h = height (m)  Loss of GPE = Gain of Ek OR vice versa  Power is defined as the rate of work done or rate of energy conversion. P = W/t = E/t where P = power (Watt——w) W= work done (J) E = energy converted (J) T = time taken (s) ** One watt is defined as the rate of work done or energy conversion of one joule per second.

Chapter 7  Pressure is defined as the force acting per unit area.  Pressure = force/area → P= F/A  SI: Newton per square metre ( N m-2 ) or Pascal (Pa)  Eg pls refer to pg 124, 125  Pressure in liquids: P=hρg In words: Pressure due to a liquid column = height of liquid of column (m) × density of liquid (kgm-3) × gravitational field strength (N/kg)  Hydraulic press works like a lever, applying a smaller effort on a small piston to lift up a larger load on a bigger piston. (Important: pg 129-131)

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05 The pressure exerted by a layer of air on the Earth’s surface is known as the atmospheric pressure. One atmosphere is 1.013 x 105 Pa (760 mm Hg) Daily application for atmospheric pressure: drinking with a straw, syringe, suction caps etc (pg 134) Barometer is an instrument used to measure atmospheric pressure. (Important: pg 135) Manometer is an instrument used to measure gas pressure. (pg 137)

** Pressure of gas supply = atmospheric pressure + pressure due to liquid column (height diff) = P0 + hpg Chapter 8  Temperature refers to how hot or cold an object is.  Heat is the amount of thermal energy that is being transferred from a hotter to a colder region.  Thermometer makes used of certain substances such as mercury to measure temperature.  Substances that have physical properties that vary continuously with the temperature are known as thermometric substances.  Physical properties that change with the temperature: (a) volume of a fixed mass of liquid, eg: mercury-in-glass / alcohol-in-glass thermometer (b)electrical voltage or electromotive force (e.m.f.), eg: thermocouple (c) electrical resistance of a piece of metal, eg: resistance thermometer (d)pressure of a fixed mass of gas at constant volume, eg: constant-volume gas thermometer  Features of good thermometer: (a) an easy-to-read scale (b)safe to use (c) responsive to temperature changes (d)sensitive to small temperature changes

(e) able to measure a wide range of temperatures  Constructing a temperature scale: (1) choose an appropriate substance, eg a column of mercury (2) choose two fixed points of hotness and coldness, 0oC & 100oC (3) set up the scale, eg divide the column into 100 equal parts  The Centigrade scale is based on simple experimental procedures that determine 2 FIXED POINTS, called the ice point and steam point.  Ice point is the temperature of a pure melting ice at one atmospheric pressure.  Steam point is the temperature of steam from water boiling at one atmospheric pressure.  Calibrating a thermometer, determining the ice point and steam point. (Important: pg 146)   oC =   -  0 x 100 (pg 147, 148)

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 The Kelvin scale (Optional) is based on the theory that there is a lowest possible temperature that exists in the universe – the absolute zero. Hence, the Kelvin scale is also called the Absolute scale.  SI unit for this scale is the kelvin (K). ** Celsius temperature/ oC = Kelvin temperature/ K – 273 (refer pg 149 figure 8.13)  A thermocouple consists of 2 types of wires made of different metals whereby the ends of the wires are joined together to form two junctions. The temperature is then calculated using the reading of the voltmeter. (pg 150-151)   where  = electromotive force e.m.f. produced   = temperature difference between the reference junction and the probe 06 Chapter 9 - 11

Chapter 12