SME
Grade 6 Science · Problem type
How fast a plate moves
Use this for “Kauai moved about 500 km in 5 million years. How fast is that?”
Diagram
Time in millions of years: 5 on the top line sits over 500 km on the bottom line: each 1 above is 100 below.
Speed in cm each year: 10
This is an example. Type your own values to start a new problem.
Distance moved
example · km
Time in millions of years
example
Speed in km each million years
worked out (not typed)
Speed in cm each year
calculated
Formulas
500 ÷ 5 = 100
Distance ÷ time = speed in km each million years
100 ÷ 10 = 10
Speed in km each million years ÷ 10 = speed in cm each year
Assumptions
•
A hot spot under Hawaii makes volcanoes, and the Pacific Plate carries each island away from it.
•
Kauai is about 500 km from the hot spot, and its oldest rock is about 5 million years old.
•
Plates move about 2 to 10 cm a year; many move about as fast as fingernails grow.
•
The speed is an average: plates creep, and faults can slip suddenly in earthquakes.
Step-by-step
WE KNOW
Distance moved: 500 km
Time in millions of years: 5
FIND
speed in km each million years, speed in cm each year
Step 1 · Find speed in km each million years
500 ÷ 5 = ?
Distance ÷ time = speed in km each million years
Share the distance over the millions of years.
Speed in km each million years = 100
Step 2 · Find speed in cm each year
100 ÷ 10 = ?
Speed in km each million years ÷ 10 = speed in cm each year
1 km in a million years is 100,000 cm in 1,000,000 years: 0.1 cm a year. So divide by 10.
Speed in cm each year = 10
Check
Put the numbers back in. Both sides should match.
100 × 5 = 500 ✓
10 × 10 = 100 ✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.