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Motion and Forces Heat and cooling Electricity Slide 2 How many significant figures? 2.00 10 3 0.00045 0.1900 Slide 3 How many significant figures? 2.00 10 3 3 0.00045 2 0.1900 4 Slide 4 Scalar or vector? Force Speed Displacement Distance Mass Work Acceleration Slide 5 Scalar or vector? ForceVector SpeedScalar DisplacementVector DistanceScalar MassScalar WorkScalar AccelerationVector Slide 6 Use this convention Up = + Right = + Down = - Left = - Slide 7 Motion You stand on top of a cliff and drop a ball. What is the sign of the balls; a) Acceleration b) Velocity c) Displacement Slide 8 Motion You stand on top of a cliff and drop a ball. What is the sign of the balls; a) Acceleration - b) Velocity - c) Displacement - Slide 9 Motion You throw a ball vertically upwards. While its moving upwards, whats the sign of its; a) Acceleration b) Velocity c) Displacement Slide 10 Motion You throw a ball vertically upwards. While its moving upwards, whats the sign of its; a) Acceleration - b) Velocity + c) Displacement + Slide 11 Newtons Laws of Motion What is Newtons first law of motion? Slide 12 Newtons Laws of Motion What is Newtons first law of motion? Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it. Slide 13 Newtons Laws of Motion What is Newtons second law of motion? Slide 14 Newtons Laws of Motion What is Newtons second law of motion? The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Slide 15 Newtons Laws of Motion What is Newtons third law of motion? Slide 16 Newtons Laws of Motion What is Newtons third law of motion? For every action force there is an equal and opposite reaction force. Forces act in pairs. Slide 17 What are the equations? Force: Momentum: Kinetic energy: Gravitational Potential energy: Work: Power: Slide 18 What are the equations? Force: F = ma Momentum: p = mv Kinetic energy: KE = 0.5mv 2 Gravitational Potential energy: PE = mgh Work: W = Fs = E Power: P = E/t Slide 19 Force graph what is the acceleration? Force (N) Mass (kg) Slide 20 Force graph what is the acceleration? Force (N) Mass (kg) a = F/m therefore, a = gradient (+) Slide 21 Heat, Temperature and Internal energy Define: 1. Heat 2. Temperature 3. Internal energy Slide 22 Heat, Temperature and Internal energy Heat Defined as the transfer of energy across a boundary due to a temperature difference. It is incorrect to say an object contains heat energy, it is correct to say internal energy Slide 23 Heat, Temperature and Internal energy Temperature A measure of how hot or cold something is. Defined from the average kinetic energy of atoms and molecules. Slide 24 Heat, Temperature and Internal energy Internal energy Defined as the energy (kinetic and potential) associated with the random, disordered motion of atoms molecules. Also known as invisible energy. Slide 25 Objects A (metal) and B (plastic) are two at the same temperature and have the same mass. AB Slide 26 If 100J of internal energy is removed from each object (A and B), will they be at the same temperature? Slide 27 No, because they will have a different specific heat capacities. Metal has a lower specific heat value which makes it more sensitive to heat transfer. Slide 28 So which object will have the higher temperature? Slide 29 Plastic B Slide 30 How did this happen? Slide 31 Thermal expansion As the temperature of a liquid or solid increases, the molecules vibrate faster and occupy more space. This results in a volume increase known as thermal expansion, thus the rails bent. Slide 32 Accommodating thermal expansion Slide 33 Equations Equation for energy associated with temperature change of an object? Equation for energy associated with phase change? Slide 34 Equations Equation for energy associated with temperature change of an object? Q = mcT Equation for energy associated with phase change? Q = mL Slide 35 Equations From Q = mL, there are 2 different L values can that be used. 1. L f = Latent heat of fusion (solid-liquid) 2. L v = Latent heat of vapourisation (liquid-gas) Slide 36 Heat transfer For each case, how does heat get transferred? 1. Table to hand 2. Saucepan to egg in boiling water 3. Sun to Earth Slide 37 Heat transfer For each case, how does heat get transferred? 1. Table to hand: Conduction, direct contact 2. Saucepan to egg in boiling water: Convection, convection currents circulating in water 3. Sun to Earth: Radiation, no medium in space Slide 38 Why? Slide 39 Static electricity Rub plastic comb with cloth Electrons transfer from cloth to comb Comb is negatively charged Comb brought near neutral paper and attracts positive charges in paper Slide 40 What is the direction of a) electron flow? and b) current? - Slide 41 - Slide 42 Series and parallel circuits 6V Slide 43 Series circuit For each bulb, R = 2 1.Voltage through each globe? 6V Slide 44 Series circuit For each bulb, R = 2 1.Voltage through each globe? 6/2 = 3V 6V Slide 45 Series circuit For each bulb, R = 2 1.Total resistance? 6V Slide 46 Series circuit For each bulb, R = 2 1.Total resistance? R(total) = R + R = 2 + 2 = 4 6V Slide 47 Parallel circuit For each bulb, R = 2 1.Voltage through each globe? 6V Slide 48 Parallel circuit For each bulb, R = 2 1.Voltage through each globe? 6V 6V Slide 49 Parallel circuit For each bulb, R = 2 1.Total resistance? 6V Slide 50 Parallel circuit For each bulb, R = 2 1.Total resistance? 1 /R(total) = 1 /R + 1 /R = 0.5 + 0.5 = 1 R(total) = 1/1 R (total) = 1 6V Slide 51 Which device is ohmic? Slide 52 Slide 53 Rest of lesson Revise through WACE book OR Revise through STAWA book