Circles in Contact Lesson 2 J.Byrne 2015

Circles in Contact Externally When circles are touching at one point on their circumference they are said to be in contact tangentially The point of contact is called the POC. The distance between the centres of the circles touching externally equals the sum of their radii Solution : 10 + 25 = 35 draw an arc of 35 J.Byrne 2015

Circles in Contact Externally Question 1 Below are two circles Green circle has a radius of 30mm Red circle has a radius of 18mm Draw a circle radius 30mm to touch both circles below. Show both POCs. J.Byrne 2015

Circles in Contact Externally Solution : 30 + 30 = 60 draw an arc of 60 30 + 18 = 48 draw an arc of 48 Join centres of circles to show POC Draw in new circle R=30 R = 60 R = 48 J.Byrne 2015

Circles in Contact Internally In the circles below they are touching internally The distance between the centres of the circles touching internally equals the difference between their radii Solution : 60 – 20 = 40 draw an arc of 40mm from centre of big circle R = 60 R = 20 J.Byrne 2015

Circles in Contact Internally Question 2 Draw a circle radius 30 mm to touch both circles below. Show all POC’s. R = 60 R = 20 J.Byrne 2015

Circles in Contact Internally Solution 2 R20 + R30 = R50 Draw an arc of 50 from centre of circle small circle R60 – R30 = R30 Draw an arc of 30 from centre of the big circle R = 30 R = 50 J.Byrne 2015

Circles in Contact Internally Join and extend all centres to show POC Draw in new circle POC POC POC J.Byrne 2015

Circles in Contact Question 3 Draw the Wine glass shown below. J.Byrne 2015

Wine Glass Construct the lines you know first. J.Byrne 2015

Wine Glass J.Byrne 2015

Light Bulb J.Byrne 2015

Draw this bottle J.Byrne 2015

Draw in what you know for sure J.Byrne 2015

Decide which circles are in contact and how J.Byrne 2015

The bottle showing all the circles and arcs J.Byrne 2015