The Plan • Part One: Measuring speed and acceleration • Part Two: Forces and Newton’s Laws • Part Three: Collisions and Energy
Part One – Measuring speed and acceleration • Goal: To find out – will the duck survive?
Units • In Physics we use the SI (Système Internationale) system of units. This metric system of units uses the basic units of metre, kilogram, second and ampere (M.K.S.A.). • There are seven basic quantities from which all others are derived.
Units QuantityUnitUnit Symbol Mass Length Time Electric current Temperature Luminous intensity Amount of substance kilogram kg metre m s second ampere A K kelvin candela cd mol mole
Units • Derived quantities are derived from the basic quantities by means of a defining equation.
Derived Units (figure out) QuantityUnitUnit SymbolDerivation Force Energy Power Pressure Electric charge EMF (electric potential) Frequency Velocity Acceleration Newton N kgms-2 kgm2s-2 Joule J kgm2s-3 Watt W kgm-1s-2 Pascal P As C Coulomb kgm2s-2A-1 V Volt s-1 Hertz Hz ms-1 ms-2
Derived Units • The word per in physics means divided by. So instead of saying speed is the metres divided by the seconds, we say metres per second. • It is written as m/s or or ms-1. • Also for simplification we use m3 instead of saying cubic metres.
Converting between prefixes • Want over got. • Convert 45nm to metres • We know 1 nm = 10-9 m • So Want Got
Standard Form • Read and highlight from notes.
Significant Figures The following have 2 sig figs. 86, 2.3, 0.56, 2.0, 0.00052, 1.7 x 10-3, 3.0 x 108 The following have 3 sig figs. 816, 2.03, 0.560, 2.00, 0.000522, 1.71 x 10-3, 3.03 x 108
Significant Figures • When working with sig figs, you can only reliably quote your answer to the level of precision of the measurement with the least number of significant figures, used in your calculation. • Eg 3.02 x 4.55012 = 13.7413624 = 13. 7 • Which was rounded to 13.7, because we can only quote 3 sig figs in our answer (because 3.02 has 3 sig figs.)
Questions Question 1 Write down the following quantities in standard form: a. 2230 m, the height of Mt Kosciusko above sea level b. 120 000 000 m, the diameter of the planet Saturn c. 0.000 84 m, the thickness of a certain piece of wire d. 0.000 000 000 25 m, the diameter of a gold atom.
Questions Question 2 State the number of significant figures in each of the following a.307 km, the distance from Albury to Melbourne b. 5.0 days, the half-life of a radioactive isotope of Bismuth c. 6.3 x 1017 m, the distance from the Earth to the star Gegulus d.0.000 902 m, the thickness of a particular sheet of paper e. 60 seconds, the number of seconds in a minute.
Questions Question 3 Paying due attention to the number of significant figures in your answer, deduce how much faster Superman is at 1.4 km/sec than a speeding bullet at 0.57 km/sec.
Questions Question 4 Which of the following would you regard as stating sin 52.4O to the appropriate number of significant figures? a) 0.7923 b) 0.792 c) 0.79 d) 0.8
Questions Question 5 Complete the following table: a. 4 kN = N b. 5 pF = F c. 22 MΩ = Ω d. 12 ms = s e. 0.7 µC = C f. 365 nm = m
Extension Question 6. Express in standard form: a. an area of 5 km2 in m2m2 b. a volume of 2 cm3 in m3m3 c. an area of 1.6 µm2 in m2m2 d. a volume of 2.5 mm3 in m3m3.
Vectors and Scalars • Scalar Only needs a number e.g. temperature, speed….. • Vector Needs a number AND a direction e.g. velocity…..
Example Place the following quantities into the correct column: Voltage, Velocity, Energy, Force, Temperature, Mass, Acceleration Vector Scalar Voltage Energy Temperature Mass Velocity Force Acceleration
Vectors • Vectors are represented by symbols in bold, or which have a line above or below them. Eg. v, v, or v . • Sometimes it easier to draw the vector as an arrow. Eg, applying a 10N force to the right 10N
Adding Vectors To add two vectors we use the rule “head to tail”. Suppose we have to add two vectors, v1 and v2 shown below
Adding vectors • How do they add?
Questions Question 7 Add these vectors Question 8 Add these vectors
Questions Question 9 Add these vectors Question 10 Add these vectors
Distance and Displacement • Distance Length an object has travelled e.g. total distance of travel Scalar • Displacement Change in position of an object. e.g. final position – initial position Vector
How do you describe direction in 1D? • Left Described with negative numbers • Right Described with positive numbers. 0 -8 -7 -6 -5 -4 -3 -2 -1 1 2 3 4 5 6 7 8
Examples • Baker starts at A and ends at B. What is his distance travelled? What is his displacement? Final Position – Initial Position -6 – 2 = -8 • Javed starts at A, and he then moves. His displacement is -4. What is his final position? -2 A B 0 -8 -7 -6 -5 -4 -3 -2 -1 1 2 3 4 5 6 7 8
Question Question 11:Thisaliis an Olympic swimmer. She swims one length of the 50m pool. a. What is her distance travelled? 50m b. What is her displacement? 50m Question 12Thisalinow swims the 50m back to complete one lap of the pool. a. What is her distance travelled? 100m b. What is her displacement? 0m
Questions • Question 13a. Grace throws a ball directly up, but doesn’t catch it on the way up. At the top of the flight, what is the distance? • b. What is the displacement? • c. As it hits the ground, what is the distance? • d. What is the displacement? 5m 1.8m
Extension questions Question 14. Krishna is following a treasure map. He moves 18m north, then 24m east. a.Draw two vectors for his movement. Add in a resultant/total vector b.What is the distance he moves? c.What is his displacement?
Extension Questions Question 15: Tim starts looking for a different treasure. He travels 20m North, then 12m west and then 11m south. a.Draw three vectors for his movement. Add in a resultant/total vector b.What is the distance he moves? c.What is his displacement?
Speed and velocity Speed and velocity are both measures of how fast something is going. Speed: Defined in terms of distance. It’s a scalar quantity. Velocity: Velocity is defined in terms of the displacement. It’s a vector quantity.
Instantaneous Speed and Velocity • Can be measured using a radar gun • Gives exact measure of speed or velocity at that precise time.
Average Speed and Velocity Can be calculated by measuring the distance/displacement and the time taken. Δ means “change in …” (final – initial)
Examples A plane flies 3000km in 4 hours. What is the speed? An athlete can run 400m in 47s. What is his speed?
Measure speed… • Small Prac
To convert from kmh-1to ms-1 To convert from kmh-1 to ms-1: To convert from ms-1 to kmh-1: ÷ 3.6 x 3.6
Questions Question 16.Usain Bolt’s record for the 100m is 9.58s. What is his average speed in m/s?
Questions Question 17: The world’s longest downhill skiing race is held in Switzerland. It is 15.8 km long and the record winning time is 13 minutes 53 seconds. Calculate the average speed of the record holder: a.in metres per second b.in kilometres per hour. Question 18: A flight from Auckland (NZ) to Melbourne takes 3.5hours. The plane has an average speed of 900km/h. What is the distance between the two cities?
Questions Question 19: Which has the greater speed?. A bird that flies 200m in 22s or a dog that runs 50m in 8s? Question 20: Kevin on a bike has a speed of 12ms-1. How many metres does he travel in 1s? In 2s? In 10s? In 20s?
Questions A frog climbing a slippery wall first leaps 80 cm up the wall before slipping down 20 cm. It then climbs another 80 cm before slipping 30 cm. Finally it reaches the top of the wall by climbing another 40 cm. Question 21: How high is the wall? Question 22: What is the distance travelled by the frog? Question 23: If the frog took 30 s to complete the climb, calculate its average velocity.
Extension Questions • Question 24:Which has the greater speed?. A car that travels 50km in 30 mins or a truck that travels 3000m in 150s? • Question 25: Explain how Usain Bolt’s top speed in a 100m sprint (calculated in Q16) is larger than his average speed
Extension Questions Question 26: A train leaves Melbourne at 9am, at an average speed of 65km/h. At 10am, a car leaves Melbourne at an average speed of 80km/h. a. At what time does the car overtake the train? b. At what distance from Melbourne does this occur?
Acceleration • When speed changes, this is acceleration • Deceleration is slowing down • Negative acceleration could be slowing down, OR accelerating in the backwards direction
Acceleration Acceleration: Change in velocity divided by time taken Change in Velocity: Final velocity – initial velocity
Examples Daniel is skateboarding at 6ms-1 and sees a dog up ahead. He slows down and stops. This slowing takes him 5s. What is his acceleration?
Questions: Question 27: Stefan (in his Lamborghini) is trying to overtake Mr McGovern in his Prius. Stefan accelerates from 10ms-1 to 20ms-1. This acceleration takes 5s. What is his acceleration? Question 28:Goran is in a drag race. He accelerates from rest to 100kmh-1 in 3.4s. What is his acceleration? (Hint: Turn 100kmh-1 into ms-1 first)
Questions Question 29: While driving, Pegah sees a duck on the road and slams on the brakes. She slows from 50kmh-1 to rest in 3.5s. What is the acceleration?