Basic Science - Physics Ms Ilana Malan – Semester One 2017 1

Unit 9 - Graphs Used for – presenting data Types of graphs and charts include bar/column graph, pie graph, dot plot, histogram, line graph, venn diagram etc Popular graphs in science are mostly line graphs and bar/column graphs

Pie Chart Organisational Chart

Column graph Pictograph

Line Graph

Graph Specifics Graph Title – Short and descriptive Axis Title – x-axis for the independent variables - y-axis for the dependent variables - include both measurement and unit - displacement (mm) Legend – identify if more than one curve on a graph Data labels – display data labels for data points Grid lines – vertical and horizontal lines on a graph Scale – chosen according information Axis data – proper intervals, include maximum and minimum variable

Graph Title – Short and descriptive Axis Title – x-axis for the independent variables - y-axis for the dependent variables - measurement and unit Legend – identify if more than one curve on a graph Data labels – display data labels for data points Grid lines – vertical and horizontal lines on a graph Scale – chosen according information Axis data – proper intervals, include maximum and minimum variable

Variables Independent: always on x-axis stands alone not dependent on any other variable/measurement Dependent: always on y-axis dependent on independent variable

Interpret a line graph Cannot see direction on a velocity – time graph Only readings that can be taken is what is on x- and y-axis Gradient: always Gradient on velocity – time graph = acceleration (+) gradient = acceleration and (–) gradient = deceleration Area on velocity – time graph = displacement

Gradient 0 s to 5 s = (change in y) ÷ (change in x) = (10 – 0) ÷ (5 – 0) = 10 ÷ 5 = 2 Gradient 7 s to 10 s = (change in y) ÷ (change in x) = (7 – 10) ÷ (10 – 7) = -3 ÷ 3 = -1

Speed/velocity: 3 m/s means the object move a distance of 3 m in a time of 1 second Acceleration: means the object’s velocity changes by 3 m/s every second acceleration with a (+) positive sign means that the velocity will increase - acceleration with a (-) negative sign means that the velocity will decrease

Example 1 An object moves from rest and increases its speed to 5 m/s in 5 s. It then turns around and keeps moving at the same speed for the next two seconds. It then accelerates again at for the next 3 seconds. It then slows down over the next 5 seconds to reach a final velocity of 6,5 m/s. Acceleration over last 5 seconds = (v-u) = (6,5 – 14) = - 1,5 m/s2 t 5 a = acceleration ; v = final velocity ; u = initial velocity ; t = time Time 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 velocity 12,5 9,5 6,5

Example 1 An object moves from rest and increases its speed to 5 m/s in 5 s. It then turns around and keeps moving at the same speed for the next two seconds. It then accelerates again at for the next 3 seconds. It then slows down over the next 5 seconds to reach a final velocity of 6,5 m/s.

Unit 10 – Energy Sources Non-renewable, formed millions of years ago under conditions that do not exist on earth today. Once they are used up they will not exist any more. Crude oil, natural gas, coal, nuclear. Emit pollution!!! Renewable, can be used over and over again as long as they are replenished. Include hydro-electric, tidal, wind, wave, geothermal, solar, biofuel. Saving energy sources – what can I/we do on a daily, monthly, annually basis in order to use less non-renewable sources, cause less pollution, use more energy efficient devices, replenish renewable sources?

Unit 11 – Electricity AC- alternating current – changes direction of flow DC – direct current – flow in one direction all the time

Basic circuit symbols

Series Total resistance = sum of individual resistors Share the total voltage Same current in all

Series Total resistance: 1 kΩ + 2 kΩ + 6 kΩ = 9 kΩ (9 000 Ω) Share the total voltage: 1 V + 2 V + 6 V = 9 V V = IR: for R1 = 1 000 Ω x 0,001 A = 1 V for R2 = 2 000 Ω x 0,001 A = 2 V for R3 = 6 000 Ω x 0,001 A = 6 V Same current in all: 1 mA

Parallel Total resistance: use formula All have the same voltage Current splits up and portion of total current flows in each resistor

Parallel Total resistance: Now answer still has to be inverted: All have the same voltage = 12 V Current splits up and portion of total current flows in each resistor:

Series and Parallel

Series and Parallel

Series and Parallel

Series and Parallel combined resistors

Example 1 Determine the total resistance: 1 Calculate series and parallel separate and 2 Try to combine resistors 8Ω and 4Ω are in series = 12Ω These two are in parallel with 12Ω(R4) thus their combined resistance is 6Ω And this combined 6Ω is again in series with 6Ω (R1) Thus total resistance = 12Ω

Example 1 Total current: I = V ÷ R (total voltage and total resistance) = 12 ÷ 12 = 1 A

Example 2  

Example 3 Total resistance: 15,875 Ω Total current: I = 0,7559 A VBC = 6,0472 V VJK = 4,5354 V VDI = VEF = VGH = 12 - (VBC + VJK) = 1,4174 V

Electric current and ammeters Measure the current flowing through a component Connected in series, no resistance

Potential Difference and Voltmeter The voltage measured across a cell/battery indicates the energy given to the charge as it flows through the cell/battery The voltage measured across a component indicates the energy given out by the charge when current flows through a component 3 V = 3 J of energy per unit charge

EMF and Potential Difference EMF is measured by a voltmeter across the cell/battery when no current is flowing, this is the maximum voltage a cell can Potential Difference is measured by a voltmeter across the cell/battery with current flowing, this is lower than emf as a result of internal resistance within the cell/battery Formula: V = IR

EMF and Potential Difference

Battery: Series vs Parallel

Example 1

Example 2 All resistors are in series thus total resistance = 10 + 20 + 30 = 60 Ω Use the formula V = IR to determine current I = V ÷ R = 12 ÷ 60 = 0,2 A

Example 3 Determine the total current

Wire a plug

Unit 12 - Radioactivity Atom: same number of electrons and protons (neutral) Ion: electrons are more/less than protons (has a charge) Negative ion: results when electrons are gained (- charge) Positive ion: results when electrons are lost (+ charge) Isotope: same element, same number of protons, different number of neutrons in the nucleus

Isotopes

Radioactivity

Uses of radioactivity

Unit 13 - Forces Forces: pulling (in front of object) or pushing (behind object) Forces can: change velocity of object, make object move, make object stop, change direction of object, change shape of object Is a vector: has both magnitude and direction

Resultant Force A resultant force is: A single force that represents or has the same effect as two or more forces acting on the same object at the same time Upward and North and to the right forces are given (+) sign Downward and South and to the left forces are given (-) sign During the calculation of the resultant force these signs are used Add all the forces acting on the object The sign of the answer indicates the direction of the resultant force

Resultant Force

Example 1

Example 2 2 N south ; 3 N North ; 6 N North ; 8 N south Determine all the forces in the same direction first: 2 N + 8 N (both south) = 10 N south 3 N + 6 N (both north) = 9 N north Thus the resultant force is: – 10 (force is south) + 9 (force is north) = - 1 N [the (-) sign indicating the direction of the resultant force is south]

Unit 14 Sound Sound is produced when an object vibrates, causing small but rapid changes to the air pressure around it When layers of air molecules are pushed close together, a compression of air particles is formed When the layers are pulled apart a decompression or rarefaction of the air molecules is formed

Production of Sound

Production of Sound

Type of Wave

Wave Properties Wavelength: the distance between one point on the wave and the equivalent next point of the same wave

Wave Properties Maximum displacement/maximum distance a wave moves from its resting position

Wave Properties Period (T): time taken for one complete wave (time for one wavelength) Frequency (f): number of waves passing a point in one second, calculate with 1 ÷ T

Loudness of sound Determined by the amplitude of a wave

Pitch of sound Determined by the frequency of a wave

Calculations

Example 1 Speed/velocity of the wave is 200 m/s Wavelength of the wave is 2 m Period of the wave is wavelength ÷ velocity = 2 ÷ 200 = 0,01 s Frequency of the wave is 1 ÷ 0,01 = 100 Hz

Example 2 Period of the wave is 4 seconds Frequency of the wave is 1 ÷ 4 = 0,25 Hz

Example 3

Example 4 Sitting on a beach an observer with a stopwatch takes the time every time a wave reaches the beach. He can see that in 3,5 minutes 3 waves reaches the beach. If the distance between successive wave crests is 11 m, determine the speed at which the waves move. Hint, you would need period/freqeuncy

Thank You.