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Forces and their effects


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Forces and their effects

  1. 1. Seisen International School Mr. Lee Grade 7 Science Tuesday, March 29, 2011
  2. 2. • Forces are pushes or pulls.• Forces act in pairs. When things touch, there are two forces acting in opposite directions.
  3. 3. The size of force is measured in newtons. You can measure the size of a force with a forcemeter.spring inside
  4. 4. Magnets produce forces that act upon each other. Theyare called attraction and repulsion.
  5. 5. Mass vs. Weight Grade 7 Science Tuesday, March 29, 2011 Seisen International School
  6. 6. Does my mass change if I leave Earth?Mass –a measure of theamount of matter in an object
  7. 7. How does my weight change on different planets?Weight – a measureof the attraction between two objectsdue to gravity
  8. 8. Location On Earth On the On In deep Near to a Moon Jupiter space black holeMass 100 kg 100 kg 100 kg 100 kg 100 kg Too big toWeight 1000 N 160 N 5400 N Almost measure. nothing Gravity is so big even light is pulled in. Nothing escapes a black hole!
  9. 9. • Which of the following are measures of weight?3/29/2011
  10. 10. Pushing Water Out of the Way• When an object is put into water, the height of the water increases• The object pushes water out of the way• The push up from the liquid is called upthrust• The upthrust force depends on how much liquid is pushed out of the way Objects feel like they weigh less in the water.
  11. 11. • Some things are “light for their size” • Ex: cork, styrofoam, balsa wood • If the object floats, the upthrust from the water is equal to the weight of the objectIn your notebook, explain why • This means the density ofit is easier to float in the calm the object is less than theocean compared to a liquid.freshwater lake.
  12. 12. • “How heavy something is for its size” • Density is a measure of the amount of substance in a given space. • The formula for density is: mass (g)density 3 volume (cm )
  13. 13. Solve this one! Suppose a substance has a mass of 10 grams and a volume of 10 ml. What is the density of this substance? 1.0 g/ml This is the density of water
  14. 14. Anything with a greater density will sink!Anything with a lower density will float!
  15. 15. Density Problem• Oil, syrup, water, 100 yen coin, cork the left side of your notebook, On draw a big picture of a tall glass showing what you think will happen when we mix all of these things together.
  16. 16. cork oil watermolasses 10 yen coin
  17. 17. • Predict what will happen when eggs are dropped in normal water and in salt water.
  18. 18. NEXT:• Finish writing up a detailed explanation (with drawings and color) of the straw and colored liquid experiment that we did last week.• Mr. Lee will come around to stamp your work when you are done.• When you are done, complete the practice questions on the next slide.
  19. 19. FRIICTTIIOnFR C On• Reducing Friction • Friction can be useful
  21. 21. M O V I N G AND STOPPING
  22. 22. Practice Questions• Read pages 45 – 49• Calculate the densities of the following:1. Oil – 100cm3 of oil has a mass of 70 g2. 25 cm3 of cork has mass of 3.75 g.3. 50 ml of syrup has a mass of 55 g.4. Does air have a density that is greater than or less than 1.0 g/ml? Explain how you know this.
  23. 23. Grade 7 Science Mr. LeeSeisen International School Tuesday, March 29, 2011
  24. 24.  Can you list 3 ways to reduce friction? Make surfaces smooth Put a lubricant on them Design the moving parts so that they roll on each other rather than slide
  25. 25.  The friction force when something slides through air or liquid is called DRAG.
  26. 26.  Friction is used to stop things moving. Car and bicycle brakes!  friction is increased Is a bald tire or a new tire better at gripping the road? Why do we prefer new tires?
  27. 27.  SPEED: tells you how far you go in a certain time What does 30 miles per hour mean? The speed of a car affects how long it takes to stop: Write a prediction about this relationship. The faster you are going, the longer it takes for you to stop! *Brake pads use the force of _________ to help stop the car
  28. 28. Turn to your neighbor and discuss thechart above. Pretend to be a teacherand a student.
  29. 29.  Use a meter stick ruler to determine if you have a faster reaction time than your group members. Do at least 5 trials and determine the average of the trials. Compare the results with your other group members. In your notebook, record the aim, results and conclusion of your investigation. Answer these questions:  What controlled variables were necessary in your experiment to conduct a fair test on each participant?  What could be a possible independent variable that could affect someone’s reaction time.  For additional points, carry out this experiment in the remaining class time.
  30. 30. Write your nameon the piece ofpaper and number1 through 8.
  31. 31.  1.What season would it be in New York in the picture shown?
  32. 32.  2.According to the picture, is it daytime or nighttime in Japan?
  33. 33.  3.What season would it be right now in Australia according to the picture?
  34. 34.  4.Name one part of the world that would be experiencing VERY LONG DAYS in the diagram below.
  35. 35. 5. How does the mass of a black hole compare with the mass of our sun?
  36. 36.  6.Explain why the Earth has stronger gravity compared to the moon.
  37. 37.  7.Study the diagram below carefully. Explain why the beeswax floats in the water, but sinks in the olive oil. Be detailed in your answer.
  38. 38.  8. Eric and Sonya are shown in the picture with a box. This question has two parts:(a) what is causing the force pointing in the left direction?(b) if the arrows are the same length, what is happening in the picture?