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Magnets, Forces & Simple Machines Review

Magnets, Forces & Simple Machines Review. Today’s Lesson. You get to listen to me talk a lot (sorry guys) We finish the write-up to our design task to Risk Assessment Early finishers find experiments we can use using dry ice (which we have) and other things close to us.

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Magnets, Forces & Simple Machines Review

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  1. Magnets, Forces & Simple Machines Review

  2. Today’s Lesson • You get to listen to me talk a lot (sorry guys) • We finish the write-up to our design task to Risk Assessment • Early finishers find experiments we can use using dry ice (which we have) and other things close to us. • We complete some experiments using dry ice

  3. First Task • Open the PPT (on wikispaces) • Write down what you don’t understand and email it to me as we go through the PPT!

  4. Properties of Magnets • The three metals which are magnetic are Iron, Nickel and Cobalt. • Magnets attract the three magnetic metals and materials that contain these metals. • In addition, one part of a magnet will always point north when allowed to swing freely. http://hackaday.com/2010/10/31/large-magnets-spark-on-halloween-who-knew/

  5. Magnetic Poles • There are 2 magnetic poles (North & South). • Magnetic poles which are opposite attract each other. • Magnetic poles which are the same will repel (push away) each other http://www.swe.org/iac/images/NewMagnet.jpg

  6. Magnetic Fields • The magnetic field is the strongest at the poles. • Magnetic field lines spread out from one pole, curve around the magnet, and return to the other pole. • All field lines will meet up with the opposite pole it came from. http://www.magnetic-shield.com/faq/interference.html

  7. Magnetic Fields • All magnets have a North and South Pole. • This can be seen through a magnetic field, which we will quickly see. • What do you think will happen to a compass if it is brought close to a magnet? • What will happen to a compass if it’s in between the North and South Pole of a Magnet?

  8. Magnetic Domain • All metals that are magnetic have a magnetic domain. • If the atoms are not pointing in the same direction, then the metal will not b very magnetic. • If most/all of the atoms point in the same direction, then it’s magnetic. http://en.wikipedia.org/wiki/File:Dominios.png

  9. Magnets In Detail • In a magnetized material, all of most of the magnetic domains (direction of magnetism) are arranged in the same direction. • A temporary magnet is a magnet that can easily lose it’s magnetism. • A magnet that keeps it’s magnetism for a long time is called a permanent magnet. • Permanent magnets can be destroyed through being heated or hit hard.

  10. Forces • Pushes and pulls are forces. • Forces can: • Change the speed of an object • Change the direction of movement of an object • Change the size or shape of an object

  11. Mass & Weight • Mass is the amount of matter or ‘stuff’ in an object. Astronauts (宇宙飛行士) in space are weightless (無重力) but still have a mass (質量). They still have bones, muscles and skin. • Weight is the name given to the pulling forces by gravity. If you are on a planet with lower gravity, then an object will have less weight.

  12. Science Math's!! • Find out the weight of the following objects for each planet: • MrFedley’s 400 g Coke Zero • Mr Snowball @ 70 KG • Shuwan @ 30 KG • 8B’s Science Homework @ 1.6 KG

  13. Newton's • All forces are measured in Newton’s. A force of 9.8 Newton’s are needed to lift a 1 KG mass on earth. • So to put it simple…. 1KG = 9.8 N • Or: 13 KG = 13 X 9.8 = 127.4 N

  14. Newton's First Law • If the forces on a mass are balanced (no resultant force), then • If it is at rest, it stays at rest • If it is moving, it keeps on moving at a constant speed in a straight line.

  15. Newton’s Second Law • Newton’s Second Law States: • Something will happen if a force is applied: the object will accelerate and the acceleration will depend on the mass of the object. • Equation: • Force = mass X acceleration • Acceleration (加速度) is the increase in speed which happens because of added force.

  16. Important Equations • Average Speed = distance travelled time taken • Average speed will not tell you the acceleration of the object, or if it is speeding up or slowing down. • Work done = force applied (N) X distance travelled (meters)

  17. Newton’s Third Law • For Newton’s Third Law: • For every action force, there is an equal and opposite reaction force. • Friction (摩擦) occurs in the opposite direction of the moving force. • Opposing force occurs in the opposite direction of gravity.

  18. Drawing Forces • Being able to draw forces is important. • The smaller the arrow, the smaller the force. • If two opposing arrows are the same size, the object is not moving or moving at the same speed. • Acceleration or deceleration occurs when one arrow is bigger than the other.

  19. Friction • Friction (摩擦) normally occurs in the opposite direction of movement. • Friction slows down an object, but also allows an object to move. • Different surfaces have different amounts of friction. Carpet has more friction than ice. A car can accelerate faster on carpet, but can also stop faster on carpet. • Sometimes, friction is good 

  20. Average Speed • Average Speed = Distance Travelled / Time Taken • Speed is a measure of how fast something moves. • Units are m/s (or cm/s, km/s etc). • EG; Lisa walked to M311 to M305 in 7 seconds. The distance between the rooms is 24 meters. • What was Lisa’s average speed?

  21. Distance Time Graph • This shows you how far something has travelled from a starting point in a particular amount of time. • If an object starts at zero and ends at zero for distance, it means the went back to the starting point. • If the distance is getting larger, it’s going away from the starting point. • If the distance is getting smaller, it’s going towards the starting point.

  22. http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr/explaining_motion/describingmotionrev2.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr/explaining_motion/describingmotionrev2.shtml

  23. Speed Time Graphs • In a Speed Time Graph, if the line is flat it is travelling at the same speed. • If the line is moving in an upward direction then the object is accelerating (getting faster) • If the line is moving in a downward direct them the object is decelerating (getting slower).

  24. http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr/explaining_motion/describingmotionrev3.shtmlhttp://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr/explaining_motion/describingmotionrev3.shtml

  25. Motion Graphs • Motion = movement • A motion graph is used to show how something moves, and how its movement changes over time. It can show: • whether an object is stationary or moving • an object's speed. • if and how its speed is changing (acceleration or deceleration). • A motion graph can show all of the above on the same graph.

  26. Continued • Time always goes on the x axis. • A distance-time graph shows how far something has travelled on the Y axis. • Distance can not go backwards. • A speed-time graph shows how fast something is moving on the Y axis.

  27. Pressure • Pressure is the force being exerted (pushed) or against (pulled) an object by something in contact with it. • As such, the area plays a very important role in how much pressure something has. • Important Equation • Pressure = force/area

  28. Pressure Continued • If you increase the area but keep the force the same, then pressure will decrease. • It’s the same as standing on one or two legs. One leg has less area touching the ground, so the pressure on one leg on the ground is higher than two legs on the ground. • Now to do some very difficult but important questions.

  29. Levers • Levers are generally ‘Force Multipliers’, which means they normally make a job easier. • There are three different classes of levers • 1st Class Levers • 2nd Class Levers • 3rd Class Levers

  30. 1st Class Levers • They have • The load at one end (what you are trying to lift) • A fulcrum in the middle • The effort force on the other end • Scissors and opening a tin with a spoon are examples of first class levers. • They are force multipliers

  31. 2nd Class Lever • They have: • The fulcrum at one end • The force at the other end • The load somewhere in between • A nut cracker and wheel barrow are good examples of 2nd class levers. • They are force multipliers

  32. 3rd Class Levers • They have: • The fulcrum at one end • The load at the other end • The effort somewhere in between • Tennis rackets and fly fishing rods are examples of 3rd class levers. • They are speed multipliers.

  33. 1st Class Levers • First class levers are force multipliers. • Having the load close to the fulcrum will have a high mechanical advantage. • Having the load far from the fulcrum will have a low mechanical advantage. • Examples include scissors, can opener, elbow etc.

  34. Second Class Lever • Second class levers go in this order. • Fulcrum • Then Load • Then Effort • Examples include nut crackers, wheel barrows and your jaw. • They are force multipliers which make our job easier. http://www.usask.ca/consumer_services/bookstore/pro_reference/anatomical_models/index.php

  35. Third Class Levers • Third class levers are speed multipliers – which means a lot of force can occur in a small area. • Third class levers go in this order: • Fulcrum • Then Effort • Then Load

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