Presentation on theme: "All scale drawings must have a scale written on them. Scales are usually expressed as ratios. Normally for maps and buildings the ratio: Drawing length:"— Presentation transcript:
All scale drawings must have a scale written on them. Scales are usually expressed as ratios. Normally for maps and buildings the ratio: Drawing length: Actual length For maps the ratio is normally in the ratio: Map distance: Actual Distance Example: 1cm : 100cm The ratio 1cm:100cm means that for every 1cm on the scale drawing the length will be 100cm in real life Example: 1:10000 The ratio 1:10000 means that the real distance is 10000 times the length of one unit on the map or drawing.
When a figure is dilated, its size is changed by multiplying the length of each side by a scale factor. All angles remain the same and so the new shape (or image) is similar to the original. Can be found by dividing a new side length by the original side length. When going from a small shape to a larger shape the scale factor is greater than 1. (Enlargement) When going from a small shape to a larger shape the scale factor is greater than 1. (Enlargement) When going from a large shape to a smaller shape the scale factor is When going from a large shape to a smaller shape the scale factor is less than 1. (Reduction) less than 1. (Reduction) 1. Determine the corresponding side lengths. 2. Determine if you are making a larger shape or a smaller shape. 3. Determine if the scale factor is greater than or less than 1. 4. Write the correct ratio.
Scale factor = new measurement old measurement -Scale factor more than 1 => shape gets bigger (Enlargement) - Scale factor less than 1 => shape gets smaller (Reduction) - Congruent shapes are similar shapes with SF = 1 Old measurement x SF = new measurement SF new old
The scale can be written as a scale factor, which is the ratio of the length or size of the drawing or model to the length of the corresponding side or part on the actual object. Scale Factor needs to be the SAME UNITS!
This HO gauge model train is a scale model of a historic train. A scale model is a proportional model of a three-dimensional object. Its dimensions are related to the dimensions of the actual object by a ratio called the scale factor. The scale factor of an HO gauge model train is. 1 87 This means that each dimension of the model is of the corresponding dimension of the actual train. 1 87
Keep like units in the same fraction. Inches = yards Inches yards
There is more than one way to set up a proportion correctly! Cross Multiply! Use common sense!
Tom is drawing a blueprint for a rectangular shed he wants to build. The scale factor is 1 ft. to ¼ inch. If the dimensions of the blueprint are 1 ¼ in. by 2 inches, what are the actual dimensions of the shed going to be?
¾ inch to 1 foot If the length in inches is 2 ¼ inch, what would the actual length be in feet ?