Circles
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Circles PowerPoint PPT Presentation


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Circles. Pi = . Pi ( π ) is a Greek letter It is a number that goes on forever It is the ratio of a circles circumference to its diameter This number is shortened to 3.14 It has it’s own button on the calculator Pi day is on the 3 month and 14 th day March 14 th

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Circles

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Circles

Circles


Circles

Pi =

  • Pi (π) is a Greek letter

  • It is a number that goes on forever

  • It is the ratio of a circles circumference to its diameter

  • This number is shortened to 3.14

  • It has it’s own button on the calculator

  • Pi day is on the 3 month and 14th day

  • March 14th

  • It is extremely important to Physics and engineering


Circumference animation

Circumference Animation


The circle

The Circle

  • The circumference is the whole way around the circle

  • The diameter is the width of the circle going through the centre

  • The radius is halfthe width


Circles

C =πd

  • I f you need to find the circumference of a circle you multiply the diameter by Pi

  • E.g.

  • Find the circumference of this circle (to 1 d.p.)

  • C = π x 7

  • C = 22 cm

7cm


Try these

Try these;

  • Find the circumference if:

  • The diameter is 12.6 cm?

  • The radius is 4.3 cm?

  • The radius is 1.6 cm?

  • Find the outer circumference of this roll of sticky tape:

3.4

1.7cm


Answers

Answers

  • 39.6 cm

  • 27.0 cm

  • 10.1 cm

  • 21.4 cm


Working backwards

Working backwards

  • If C =πd,then we can work out the diameter if we are given the circumference

  • E.g.

    C =πd

    52= πd

    We need to divide 52 by π

    D= 16.6 cm

Circumference= 52 cm


Now try these

Now try these;

  • Find the diameter if the circumference is;

  • 85 cm

  • 12.6 cm

  • 25.3 cm

  • Find the radius if the circumference is;

  • 200m

  • 400m


Answers1

Answers

  • 27.1 cm

  • 4 cm

  • 8 cm

  • 31.8 m

  • 63.7m


Area animation

Area Animation


A r 2

A =πr2

  • Like most areas you need to multiply two sides together, this is where the r2 comes in, but for a circle you have to multiply this by pi

  • E.g.

  • Find the area of this circle:

  • A =πr2

  • A =π x 7.42

  • A = 54.8 xπ

  • A = 172.2cm2

7.4cm


Try these1

Try these;

  • Find the area if;

  • The diameter is 25.2 cm?

  • The diameter is 10 yards?

  • A CD is made from plastic. Find the area of plastic in this CD;

12 cm

1.5cm


Answers2

Answers

  • 498.8 cm2

  • 78.5 yards2

  • 111.3cm2


Working backwards1

Working backwards

  • If A =πr2 then you can find the radius if you have the area

  • E.g.

  • 500 = πr2

  • Divide 500 byπ to find out what r2 is

  • 159.2 = r2

  • This is not the radius, but the radius squared, so we need to square root our answer

  • R = 12.6 cm

Area = 500 cm2


Now try these1

Now try these;

  • Find the radius if the area is

  • 34 cm2

  • 200mm2

  • Find the circumference for both circles


Answers3

Answers

  • 3.3 cm

  • 8 mm

  • 20.7 cm

  • 50.3 cm


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