So this past weekend me and a couple of friends went down to a park converted from a landfill. Now the only question remaining is what you do at this kind of park. There is only one thing you can do, box sliding. This entails getting a very large piece of cardboard and diving down a hill over coming friction and speeding down the hill. The reason you use cardboard is because it has a lower coefficient of friction making sliding easier. If you chose not to use cardboard you would find your shirt ripped up and a lot of burns on the front of your body. Your weight and initial momentum wouldn't allow you to go much further than a few feet. The physics behind box sliding is fairly simple. You push off from the the top of the hill and start moving down. The cardboard has lower friction causing a longer ride. You continue to move down accelerating as the force of weight and normal force overcomes the force of friction. You continue to slide at a fairly constant rate until the hill starts to taper and friction force starts to overcome weight and normal force slowing the box usually faster than it slows you causing you to hold on tight until both you and the box come to complete stops.

Thanks for reading, Mark.

PS. I was going to post a video of box sliding but I haven't been emailed it yet. I'll put that up later.

Floating Yen

Since my trip to Japan the one Yen coin has fascinated me. It’s surprisingly light even though it’s about as big as an American penny. It weighs about as much as half a dime yet its about twice as big as a dime. It has a large volume for such a small weight. Therefore when it is placed on the surface of the water with most of its volume submerged, it floats. The volume of the piece submerged is great enough so the force of the water pushing up on the 1 yen is equal to the force of weight pushing it down. Another interesting fact about the one yen coin is that it only floats because of surface tension. Without surface tension the one yen sinks to the bottom, which means the force of surface tension is fairly greater than the force of the underlying water up to a certain point.

Thanks for reading, Mark.

Torque - 2438a

On Veteran’s day we had the VEX Robotics Competition at Iolani, so I took the robot home to program it’s autonomous programming. The video to the left not only demonstrates the program, it also demonstrates torque. Each of the wheels and the conveyer belt has a motor which turns an axle. The wheels want to resist the turning of the motor because of friction. The motor applies a set amount of force on the square axle in either a counter clockwise or clockwise direction. The wheel, which contacts the ground or the bearing blocks holding it in place creating a force in the opposite direction of friction. This causes the wheels to move slower, even though the motor is applying constant force. Because of the motor is applying constant force the motor can break because the torque countering the motor is too much. This is why there are gear reductions on the robot to effectively increase torque while lowering speed and stress on the motors.

Thanks for reading, Mark.

(The video is of Iolani Robot 2438a, shot in my garage)

Newton's Cradle

This morning I decided that I wanted to try using the Newton’s cradle thing to show rotational movement, but it was tangled so I’ll just have to explain it. The force of weight increases and decreases the velocity as it moves up or down the curve giving it a tangential acceleration at certain points of the curve. Tension then counteracts weight and pulls the ball radially inward which is weakest at the apex of each side and strongest at the bottom of the rotation. When it strikes another ball the ball transfers its energy this continually happens until the final ball is given force and velocity to travel forward into a circular path. This is a very basic view on how Newton’s cradle works but its essentially conservation of energy and circular motion. This is a picture of something suspended by a strap moving in a circular path, tension up and weight down. It follows the circular path drawn.

Circular Motion

Since the discovery of gravity, force, and centripetal force, people have figured out how to orbit things from bullets to rockets. Whether they could apply enough force is the difference. Places like JPL create modules to create enough force and the velocity to counteract the radially inward force creating an orbit. Gravity has such a huge effect on satellites and rockets that it requires a lot of force to even get up to orbiting speed. What causes the orbit is gravity pulling the rocket inward while the rocket pushes it forward. This causes a circular path around the earth. If you get to a high enough orbit, the satellite can move at the same rate as the earth spins causing a stationary orbit. To get out of orbit it needs to get to orbiting speed of 7.5 km/s and it needs to overcome the force making its vector greater than the circle.

Thanks for reading, Mark.