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Friday, August 18, 2017

Why are Astronauts "weightless" in the space station?

This is easily one of the biggest MISCONCEPTIONS there is in science!!! A good majority of people would guess because there is no gravity in space....NNNNNOOOOOOO!!!!!


So if there is a lot of gravity acting on the astronauts from the earth, how can they float???

It is actually because all satellites are constantly FREE FALLING towards the earth, because of gravity. And if you are on a scale in an elevator that is free falling, guess what the scale would read....0!! You would be 'apparently weightless' because everything falls with the same acceleration when gravity is involved. You would not be truly weightless, since there is still gravity acting on you.

Check out this really good video from the Veritasium channel.

How do Satellites Work? The very basics...

Satellites are cool and help make modern life possible, but they are also confusing to many people - how can these things stay in orbit for decades without crashing into the earth?

The key ideas come from projectile motion. Gravity creates acceleration downward, but we need to give a fast enough speed perpendicular to gravity so the satellite moves in a curve. If you play with that speed, what you'll find is that there is a special speed where, as it falls, it moves very far forward. The trick is to have the curve of the satellite match the curve of the earth - thankfully the earth is more or less round!! This special speed is called the orbital velocity.

Check out the video, and I hope it helps!

Understanding some Properties of Projectiles

Forget the math for a few minutes - focus on some of the important concepts and interesting properties of projectiles, at least under ideal conditions (i.e. no air friction!). This gets into the importance of independent horizontal and vertical motions that are really the key to understanding projectile motion, and multi-dimensional motion in general. To understand why parabolic paths form, check out this video. To check out some basic math for projectile problems, check out this video.

Check it out, and hopefully this will make some sense to help you understand what the math is telling us when we do problems.

Thursday, August 17, 2017

Projectile trajectories - With and Without Air Friction

All of us are familiar with the arch-shaped path, or trajectory, a ball follows when we throw it. When symmetric, this is a parabola, and is the common shape we use in physics classes for projectiles. But WHY is it an arch of any kind, let alone a parabola? And why are we lying to you about projectiles???

We ignore air friction when we do projectile problems, but in life this makes it more complicated, and also no longer a perfect parabola. Check out this video to get a sense of why parabolas form when there is no air friction, and what the trajectory looks like in a more realistic environment, with air friction.

How to do Relative Motion problems: Getting across a moving river

Relative motion has to do with multiple objects moving with respect to one another, and trying to think about how it all looks depending on what point of view different observers have when watching the objects.

A classic example of this is trying to get a boat across a flowing river, without being pushed off-course or downstream. How is this done? This is the same problem as trying to fly a plane when the wind hits it from the side, or a bird trying to fly on a windy day. What do you have to do to the boat, airplane or bird in order to not be pushed off-source?!

Check out this video to see how to use basic vector rules with the velocity vectors involved in the problem!

How to do Projectile Motion problems

Projectiles are objects that fly through the air or space, under the influence of gravity (and ignoring air friction for now), but not using any of its own energy to do so. It has been 'projected' by something else to start moving, like kicking or throwing a ball, shooting an arrow, a satellite, or even when you run and jump - you're a projectile once in the air!

Projectiles follow an arch, which is technically a parabola when there is no air resistance.

The key to understanding this motion is to realize there are two motions simultaneously: constant horizontal velocity, and constant vertical acceleration due to gravity. And when two things are perpendicular to each other, they are also independent of each other. Sideways motion could care less about what happens vertically, and vice versa!

Check out this video, which goes through two related projectile problems, and how to set them up.

Tuesday, July 18, 2017

Chem/Phys Reunion in September!!

We will have a Chem/Phys reunion on September 23, at ETHS. We are trying to get as many alums from as many decades as possible, and current students will be a part of this as tours of the classrooms and schools will be coming through. It can be a wonderful chance to meet people who were in your same seats years ago, and also start networking prior to going to never know when there might be a summer internship or connection at a school you are looking at, etc. Save the date! And if a parent or sibling is an alum, pass this along! Check out