







Distance between a chord and its arc on a circle 
20180323 

From Doug: Specifically, what is the subject distance for the Earth orbiting for 27 days. Assume the orbit of the Earth to be a circle have a 93 million mile radius. Assume the angle of arc to be (27/365) x 360 degrees. Thank you. Answered by Penny Nom. 





Compressed Earth blocks 
20160302 

From John: how many 14"x10"x4" blocks do I need for a 1300sq foot house 8 foot high Answered by Penny Nom. 





Prove the earth is round 
20160130 

From Kevin: Working on a project for a science fair.
To prove the earth is round without the ability to get way above the surface.
How could we set up and experiment to see the curve.
My thought is using a telescope at the beach?
Form what we see so far the curve is 8 inches per mile?
So thought is set up a telescope and a target 1 mile away? Answered by Robert Dawson and Chris Fisher. 





How much does the Earth curve over a one foot distance? 
20151124 

From Sean: Hi, I am trying to figure out how much the earth curves over a one foot distance. I'd like to be able to draw the exact arc on a piece of paper. I am an artist and am looking to make glass vessels with the exact curvature of the earth. I read on your site that it curves approximately 8 inches per mile. can I just use simple ratios to break it down into inches?? Thank you so much for your help. Answered by Harley Weston. 





Curvature of the Earth 
20141229 

From Jimmy: Both batteries died in my scientific calculator and I have lost my formula for the heigth of the curvature of the earth between two points on the surface. I used degrees and miles. I only had to enter the distance between the two points on the surface and the formula gave me the hieght the earth raised between the two points. Answered by Robert Dawson. 





An arc subtended at the center of the Earth 
20140720 

From Abhinav: Meerut is 60 km from Delhi. Find the nearest second the angle subtended at the center of the earth by the arc joining these two points,earth being regarded as a sphere of 5940 km radius. Answered by Penny Nom. 





A triangle on the surface of the Earth 
20140626 

From Christine: A, B and C are three towns, the bearing of B and C from A being 310 degrees and 220 degrees, and their distances from A are 510km and 700km respectively. Find the bearing of B from C to the nearest minute. Answered by Robert Dawson. 





A model of the sun and the Earth 
20140614 

From Lynn: There is a model of the sun that is 2 1/2 inches in diameter. This is the only clue we have! How far away is the earth from this model? Answered by Penny Nom. 





Curvature of the Earth 
20140328 

From Max:
Recently I read the answer to a question proposed by someone on this site.
The question : What is the rate of curvature per mile on Earth?
The answer given : Use Pythagoras' Theorem to solve for the answer, given a 1 mile side
and a side as the radius. The hypotenuse minus the radius is your answer of drop/mile or curve/mile.
My conjecture : Why go through all of that work if the distance is one? Something like
{1/diameter} would would fine for such a problem. Seems like a lot of work for no reason.
I understand the practical application of Pythagoras' Theorem in this certain situation, as you would need
to use a^2+b^2=c^2 for any distance greater than one [mile]..
It just seems excessive and unnecessary if you're solving for curve / one mile. Answered by Robert Dawson. 





A cable around the Earth 
20140313 

From fikile: By how much must an equatorial cable be extended in order that it runs 1meter above the ground? Answered by Penny Nom. 





If the earth was made of a ball of string 
20130918 

From Tammy: My 9 year old son asked me a question and I have no idea how to work it out! Please can you help?
If the earth was made of a ball of string and you unravelled the string how long would it be? Assuming the string is 5mm thick. Answered by Penny Nom. 





The curvature of the earth 
20120208 

From sean: Question from sean, a student:
Two people 1.8 metres tall walk directly away from each other until they can no longer see each other (due to the curvature of the earth, which has a radius of about 6378 km).
A) Find a function relating the height of two identical objects with the distance between them using the scenario above as an example.
B) Sketch this function (you may use Graphmatica if you wish). Over what domain and range does the function exist?
C) Describe this relation in practical terms. Answered by Harley Weston. 





A tangent to the earth 
20110903 

From Vickram: I have a math problem regarding tangent and circle. My example is as
follows: if a long flat ruler measuring 1500 miles is placed on top of earth
which has a radius of 3960 miles what part (length) of the tangential ruler
will actually be touching the earth and what two parts will not? Answered by Chris Fisher. 





The volume of earth to be moved 
20100729 

From Michael: Volume of earth moved @ 500' across, 1 to 3 degree slope, 30' deep X 50' across at the bottom. Answered by Stephen La Rocque and Harley Weston. 





Curvature of the Earth 
20100529 

From grant: if you have 2 plumb structures 10ft. tall, how far apart will they be when they are 1 inch out of parallel at the top Answered by Tyler Wood. 





Line of sight 
20100506 

From David: I live in St. Joseph, Michigan and there is an ongoing argument regarding lineofsight over the horizon.
Standing on a 200 foot high bluff here, people swear they can see the top of the Willis (nee Sears) Tower in Chicago, which is about 1653 feet high.
It is my contention that this is actually a "refracted reflection" and not directlineofsight.
So, to settle the argument, I'd sure like some simple explanation for this, even ifand I hope notI am incorrect.
David Answered by Harley Weston. 





If the earth were covered completely with water 
20100225 

From don: If the earth were covered completely with water (over Everest) how many gallons would it be?? Answered by Penny Nom. 





Everything in a cube 2 miles long? 
20100131 

From Naresh: in a book, i got to read this :
Is it possible to pack the entire population of earth and everything that was created by
humankind in a cube whose edges are 2 miles long ?
Is it possible? Thanks. Answered by Stephen La Rocque. 





A string around the world 
20080818 

From Terry: I heard this on T.V. and was wondering if it was true. Place a string around
the world, you would need 25,000 miles of string. If you raised the string
off of the ground by 1 foot all the way around. How much more string
would you need? Answered by Penny Nom. 





The weight of a cubic yard of dirt 
20080721 

From Robert: I need to know how many pounds of dirt is in a cubic yard Answered by Penny Nom. 





How far away is the horizon? 
20080613 

From Ali: A plane is 10km above the earths surface, and you want to know how far away the horizon is, you know that the radius of the earth is about 6400km, how far away is the horizon along the earth's curved surface. My teacher has drawn a diagram; a circle representing the earth with one vertex at the center of the earth, another vertex outside the cirlce representing the plane (the distance between the earth and plane is 10km) and the last one is on the circle representing the horizon. Could you please explain how I would solve this problem, thanks! Answered by Penny Nom. 





Throwing a ball on the moon 
20080521 

From leria: equation for motion of moon is h=2.67t^2 + vt + s
equation for earth h=16t + vt + s
Suppose you are on an outpost on the moon and Jan is back on Earth. Both people toss a ball from a height of 96 feet with an initial velocity of 16 feet per second. How much longer will your ball stay in motion on the moon than Jan's on the earth?
Math Central,
I'm having a difficult time understanding which numbers to plug into the formula. Answered by Stephen La Rocque. 





Distance seen 
20080318 

From Nev: formule: Distance Seen
S = 1.225 x square root of H
S = Distance seen in Miles
H = Height in Feet
What dose 1.225 Relate To ? Answered by Stephen La Rocque. 





The distance to the moon from earth 
20060519 

From Maira: Using trigonometric functions first, show how to find the distance to the moon from earth and then find the radius of the moon. Answered by Stephen La Rocque. 





How far from Earth is Neptune? 
20060321 

From Scott: A laser beam travelling at the speed of light bounces off the planet Neptune and returns to Earth in 29 960.72 s. The speed of light is 299 792.5 km/s. How far from Earth is Neptune? Answered by Penny. 





The volume of the earth in gallons 
20050818 

From Daniel: I would like to know how to find the volume of the Earth in gallons. Answered by Penny Nom. 





Difference in latitude 
20050405 

From Gretel: Assuming the the earth is a sphere of radius 6378 kilometers, what is the difference in latitude of two cities, one of which is 400 kilometers due north of the other? 500 kilometers? Answered by Penny Nom. 





How far can you see? 
20031215 

From Judy:
How far apart, assuming no obstacles, can two people stand and still see each other?
i know this deals with the curvature of earth, but i can't figure out the formulas involved.
Answered by Chris Fisher. 





The volume of an earthen pit 
20030912 

From Bruce: This shape would occur at the four corners of a rectangular shaped earthen pit with sloping sides (1:1.5). Depth is 14'. Top dimensions are 170' by 158'. After calculating the easy volume components of this shape, we are left with the end corner pieces. 21' base, 14' height, side hypotenuse 25.24' and corner diagonal 32.83'. We're confused. Thank you for any help you may provide. Answered by Penny Nom. 





Hidden by the curvature of the Earth 
20030423 

From Shirley: There are 2 six foot men. What would the distance be between them before one could not be seen because of the curvature of the earth? Answered by Penny Nom. 





Wrap a rope around the equator 
20030212 

From Ali: If you take a rope and wrap it around the equator and then overlap it 6ft. and cut off the extra then you loosen it up so the ends meet how far would it stand off the ground? Answered by Penny Nom. 





The entire earths' population would fit in the state of Texas 
20020918 

From Roz: I have been told that the entire earths' population would fit in the state of Texas and each person would have 1/2 acre. Is this true. Answered by Chris Fisher. 





Ratios and weights on Neptune 
20020603 

From Janice: The ratio of an object's weight on earth to it's weight on Neptune is 5:7. How much would a person who weighs 150 pounds on earth weigh on Neptune. Answered by Penny Nom. 





When will the ship disappear? 
20011010 

From Stacy: If the sail of a ship were a 100 ft. tall and you were a mouse at the edge of the shore looking out at it, how far out would the ship be when it disappears? ( your eye level is level with the water.) Answered by Harley Weston. 





Earthquake warning 
20010903 

From Dillon: In the city of Skangai there are 6 million people.Each person has to tell 2 more people that theres going to be an earthquake. After they do they leave the city. There will be no duplications.It takes 3 minutes to tell each person. How long will it take for the whole city to know about the earthquake? Answered by Penny Nom. 





Mass of the earth 
20000221 

From Terry Broughton: My name is terry i am 15 my question is how much does our planet earth weigh ? Answered by Chris Fisher and Harley Weston. 





Curvature of the Earth 
19980316 

From Robert Dyck: How can I find the curvature per mile of the earths surface? What is it? Answered by Harley Weston. 





The Earth's Arc 
19980206 

From Robert Dyck: How do I find the arc/mile of the earths surface? What is the arc? Answered by Harley Weston. 

