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Help I am under lots of pressure!

Help I am under lots of pressure!. Topics that have been covered. Forces Particulate model of matter Mass, weight and density. Air has weight. Pressing Problem.

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Help I am under lots of pressure!

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  1. Help I am under lots of pressure!

  2. Topics that have been covered • Forces • Particulate model of matter • Mass, weight and density

  3. Air has weight

  4. Pressing Problem • Suppose the thin film of ice gave way and this girl has fallen through the ice in the pond. There is no means of getting help to her other than yourself. Would you walk or crawl to her?

  5. Walking • Let your weight be 55kg. The force on the ice will then be 550N whether your walk or crawl.( g is 10 N/Kg) • Weight will mostly be on one foot at any one time. We supposed that your foot is rectangle. Foot 0.10m 0.20m

  6. Crawling • Assume you lie flat on your stomach when crawling and we assume your body to have the shape and measurements shown. BODY 0.25m 1m

  7. Comparison • To make a fair comparison we will have to consider the same area of ice in each case. • 1m2 will be a convenient area. • For crawling, • A force of 2200N will be exerted on every square metre of ice. • For walking, • A force of 27500N will be exerted on every square metre of ice.

  8. Definition of pressure • Pressure is defined as force per unit area. (here 1m2) • Pressure, P = Force, F Area, A Where force F is in newtons (N) area A is in m2 pressure P is in pascal (Pa) or N/m2

  9. Semi trailer

  10. Who will you bring as your dance partner?

  11. Bed of nails

  12. Suction cup • Suction cup

  13. Atmospheric pressure • Atmosphere is a layer of air surrounding the Earth • Extends up to 1000km above the surface of the Earth • Weight of the atmosphere exerts a pressure on the surface called atmospheric pressure. • The pressure exerted by air molecules at sea level is 1.013 x 102 Pa • This is equivalent to placing a 1kg mass(10N) weight on an area of 1cm2

  14. Drinking from a straw • Atmospheric pressure is acting on the surface of water inside the cup. • When you suck, you are reducing the pressure in your mouth. • As a consequence, the atmospheric pressure pushes the water from the cup into your mouth.

  15. Rubber sucker • Rubber suckers are used at home to hang clothes • The suckers are pressed in to force out the air within to create a partial vacuum • The greater external atmospheric pressure acts on it to keep it in place Partial vacuum

  16. Question??? • How will a swimmer feel in his ear drums as he dives deeper into a swimming pool?

  17. Work problem • Find the pressure acting on a diver when he is at the surface Given density of water =1000kg m-3; acceleration due to gravity =10ms-2; atmospheric pressure = 1.01x 105 Pa

  18. Work problem • Find the pressure acting on the same diver when he is 15 m in the water

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