1 / 29

CHAPTER 6

CHAPTER 6. On the Move What you should have completed so far: Distance Vs. Displacement sheets Text questions 1-8 on 140-141 on speed and velocity. Acceleration questions. The practical on measuring and graphing speed. The 3 page worksheet on interpreting graphs.

bud
Download Presentation

CHAPTER 6

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CHAPTER 6 On the Move What you should have completed so far: Distance Vs. Displacement sheets Text questions 1-8 on 140-141 on speed and velocity. Acceleration questions. The practical on measuring and graphing speed. The 3 page worksheet on interpreting graphs. The practical on the Ticker timer with both tables of results completed and the questions. If NOT YOU HAVE TO SEE ME IN in my office AT 1pm on Tuesday & Wed so I can help you finish the work.

  2. Recap- Speed Vs Velocity Speed is scalar. Scalars are quantities with only magnitude. The direction does not matter. If you are on the highway whether traveling 100 km/h south or 100 km/h north, your speed is still 100 km/h. Distance traveled / Time taken (remember to write the units also and make sure you are able to convert numbers also to get the correct answer) Ex 1: Ruby walks 2 km in 30 min on her way home from school. What is her average speed for the trip in m/s. Ex 2: You drive a car for 2.0 hr at 40 km/h, then for another 2.0 hr at 60 km/h. a. What is your average speed? b. Do you get the same answer if you drive 100 km at each of the two speeds?

  3. Ans • 2 a. The total distance driven = [(2 h )(40 km /h) + (2 h)( 60 km/h)] = 200 km The total time = 2 + 2 = 4 h average speed = (200 km)/(4 h) = 50km/h • 2b. total distance = 100 + 100 = 200 km total time = [(100 km)/(40 km/h) + (100 km)/ 60 km/h)] = 4.17 h average speed = (200 km)/(4.17 h) = 48 km/h

  4. Velocity Velocity is a vector. Both direction and quantity must be stated. If one train has a velocity of 100km/h north, and a second train has a velocity of 100km/h south, the two trains have different velocities, even though their speed is the same. Displacement (change in position) / Time taken. (It is different to speed as there is a directional component.)

  5. Question: A hiker traveled 80.0 m [S] at 1.00 m/s, then 80.0 m [S] at 5.00 m/s. What is the hiker's average velocity? Question: What if Ruby’s journey home involved her walking from school. 0.5 km north to Sarah's place, to deliver Sarah's homework and then walking 1.5 km due south to her own home, in 2 hours. What’s the displacement and velocity?

  6. Answers Answer:
displacement = 160.0 m [S]
time for the first part is 80.0÷1.00= 80.0 s, time for the second part is 80.0 m ÷ 5.00 m/s = 16.0 s. 
Total time = 80.0+16.0 = 96.0 s
Therefore, the velocity is (160.0 m [S])÷96.0 s = 1.67 m/s (S)

  7. Gravity's pull on objects is a constant here on Earth (an object will fall at a constant acceleration of 9.8 or 10 m/s2) and it always pulls toward the center of the planet (Note: Gravity decreases as you move far away from the surface of the planet.). We can see how quickly an object gains speed as it falls. It travels at about 10 m/s after one second, 20 m/s after two seconds, 30 m/s after three. This translates to speeds of about 36, 72 and 108 km/h after just three seconds. Objects won’t really fall quite this fast for the same reason that a feather and a rock won’t hit the ground at the same time when dropped together. Air resistance will slow them to some extent. Terminal velocity- These 2 sky divers will reach what is called Terminal Velocity which is the maximum speed where the acceleration is zero. This happens when the downward force due to gravity is equal to the upward force of air resistance. The terminal velocity of the sky divers can increase if they change their body shape.

  8. ACCELERATION What’s acceleration: the rate of change in speed or velocity. A= Change in Speed/ Change in Time In the graph below (right) what is the acceleration of the sprinter in the first 30 sec?. A car speeds up from 8 m/s to 18 m/s over a period of 20 s. What is its acceleration in m/s2? What is deceleration?

  9. Forces on a car Engine pushes forward Resistance forces that push against the direction of movement: Drag etc. pulls back (air resistance and friction) (Horizontal forces only shown)

  10. Forces on a car Road pushes up Engine pushes forward Resistance forces that push against the direction of movement: Drag etc. pulls back (air resistance and friction) Weight pulls car down

  11. NEWTON’S FIRST LAW OF MOTION • An object will remain at rest or will not change its speed or direction unless it is acted upon by an outside, unbalance force • Also known as the Law of Inertia; inertia is the scientific principle behind why we wear seat belts. Inertia makes things difficult to stop as well as hard to get started. • All objects possess inertia or a tendency to resist change. The larger the mass, the greater the inertia. This is why it is much easier to stop an empty runaway shopping trolley than a full one. Coins on elbow trick! How does it work according to this law? http://www.youtube.com/watch?v=NWE_aGqfUDs&feature=related Lego one http://www.youtube.com/watch?v=7_fbH-muvlw&feature=fvw

  12. NEWTON’S FIRST LAW OF MOTION is not always apparent. • Friction and air resistance are always present • You don’t always realise you’re moving! • Is it your train moving forward, or the one next to you going backwards? • You can get a false sense of security in a car.

  13. ACTIVITY • LOOKING AT INERTIA (Pg 148) • FORCING THE ISSUE (Handout) • EXPERIMENT: Crash test dummies • EXPERIMENT: Inertia in Motion

  14. CRASH TEST DUMMIES

  15. FORCING THE ISSUE HANDOUT Situation 2: Situation 1: A. A. B. A B, Describe what would happen in these situations to the people in trolleys A and B.

  16. FORCING THE ISSUE HANDOUT Situation 1: Situation 2: Describe why it is possible to perform the following tricks

  17. Crash testing Ready Set Go! Source: http://www.inrialpes.fr

  18. Crash testing Ready Set Go! Source: http://www.inrialpes.fr

  19. NEWTON’S SECOND LAW OF MOTION The mass of an object affects the way that it moves when acted upon by one or more forces a= F/ m The mass of the object (measured in kg) The total force of the object (measured in Newtons- N) Acceleration (measured in meters per second squared- m/s )

  20. NEWTON’S SECOND LAW OF MOTION • Describes the fact that larger masses accelerate less rapidly than smaller massed acted on by the same total force • Can also be expressed as F= ma Force=Newtons Mass=Kg Acceleration=m/s/s • If the mass of the brick and car is 2kg and the force applied is 4 newtons, what is ‘a’?

  21. NEWTON’S THIRD LAW OF MOTION For every action there is an equal an opposite reaction When an object applies a force to a second object, the second object applies an equal and opposite force back to the first object

  22. ACTIVITY • Think about three examples that demonstrate an action – reaction forces • Pushing off a starting block. Action- the push and the Reaction- is the block pushing back • Pushing water while swimming- water pushes back on your hands as you swim • http://www.wonderhowto.com/how-to-demonstrate-newtons-third-law-motion-223910/

  23. WORK DONE • When ever you apply a force (a push or a pull. Measured in Newtons) to an object it moves in direction of that force • Energy is the capacity of something to do work and there are many types of energy (gravitational, electrical, heat, potential, kinetic). Energy can never be created or destroyed (this is the Law of Conservation of Energy), it just changes from one form to another. • Work is another physical term. Work is done on an object when a force is applied over a distance. If an object does not move then work done= 0. Work is measured in joules (like energy) Work Done (newton*meter= joules) = Force (N) X distance travelled in the direction of the force ( M)

  24. Think pg 155 - answers • A) Gardener pushes with a horizontal force of 300 N, the lawnmower moves 5meters across the lawn. Work done = F x Distance = 300 x 5 = 1500 Nm

  25. Think pg 155 B) Three people try to push a car out of a mud bog. Each person pushes with a force of 400 N , however the car does not move. Work Done = F x distance travelled = 400 X 0 = 0

  26. Energy transformations • Energy can be transformed from one form to another, for example: • Fuel (chemical) energy to kinetic energy • Gravitational potential energy to kinetic energy • Kinetic energy to heat • Etc.

  27. Conservation of energy • When energy is transformed from one form to another, the total amount of energy remains the same. • This is a very useful principle if you can identify where all the energy has come from and where it is going.

More Related