Last summer I went to the Cedar Point amusement park in Ohio and was particularly interested in the physics behind one of the rides called the twister. This roller coaster consists of two identical towers that spiral upward parallel to each other. The ride starts when the cart is shot up one side. From here the cart rolls back down and with its own energy shoots back up the other side. The ride has been calculated to reach close to the top of the tower, but not fall off. This calculation was completed by using the equation ΔKE = −ΔPE +WNC. By calculating the correct speed of the cart upon takeoff as well as factoring in the non conservative forces such as friction and air resistance, the makers of this ride are able to determine how high the cart will go. Since no new outside forces act on the cart after its initial launch, the cart will only reach a slightly smaller height on the other tower, therefore ensuring the safety of the riders.

The physics of the spinning Earth

In 2014, Vsauce created a video that can almost entirely be explained by what we have learned about torque, inertia, and angular momentum.  For example, at the beginning of the video that every object at the equator of the earth is spinning at 465 m/s due East while he in San Francisco is spinning 368 m/s due East.  This can be explained by our equation for angular velocity and the fact that the earth is a sphere.  The radius of a sphere maximizes at a line that perfectly circulates its center, which on Earth is designated by the equator.  San Francisco is not at the equator, thus the radius of the circle that it is spinning around is smaller than the radius of the equator.  So, while both an object on the equator and San Francisco may have the same angular velocity, the larger radius of an object on the equator creates a larger linear velocity for it in comparison to San Francisco according to v = w*r.  Here is the link to the video: Vsauce Video, I highly advise everyone sees it, as Vsauce makes some interesting and well-made material.

Impulse Saves

As a hockey goalie, it is no secret that I am trying to get hit with pucks as frequently as possible. Recently, in the spirit of physics, I was wondering how my protective equipment protects me. Pucks are shot on average at 75 mph, which means they hit me with a momentum of  5.7 kg*m/s. The

p = m*v = (.170 kg)*(33.528 m/s) = 5.7 kg*m/s

So why is it that goalies aren't always completely covered in bruises? My CCM chest protector is made with D3O foam, a high-tech, shock-absorbing material. It is an engineered material that acts as a non-Newtonian fluid. What this means is that its viscosity depends on the force applied to the material. In the case of D3O, it is more "squishy" when you press on it gently and hard when hit with a puck (or hammer), this is called "shear thickening."

 

A non-Newtonian fluid is useful in protective equipment because they absorb the impact of the force by spreading it through the material and by increasing the surface area over which the force is applied. This does three things: 1) increases the time of the impulse, which reduces the force and 2) increases the surface area, which decreases the pressure, reducing blunt trauma caused by the impact (bruises), 3) allowing for the dissipation of energy through friction between D3O molecules. As we have seen in in-class problems, even a small increase in time can drastically reduce the force. 

1) F = m*(vf-vi) / t             2) P = F / Area

While the physics of Non-Newtonian fluids can become very complicated, it is these introductory level relationships that govern their use as protective equipment in sports. 

Additionally, there is another way that goalies increase the time of the impulse. As a goalie, you are taught not to be "scared" of the puck. Being scared of being hit causes you to tense up, therefore decreasing the impulse time (in addition to psychological factors). When you are not afraid of being hit, you can focus on reacting and "cradling" the puck, further increasing the impulse time and decreasing the force experienced (see video below @ 2:07). 

Sources:

http://www.explainthatstuff.com/energy-absorbing-materials.html

https://www.d3o.com/

http://www.physics.org/featuredetail.asp?id=35

Formal Szn

While I was at the Corral, I witnessed multiple people slip and fall (for various reasons). One of these individuals stood out to be because of how close he fell to me and through my laughter I started to wonder how much force he hit the ground with.

This individual is 5"8 and 205 pounds (1.73 meters and 92.99 kilograms):

The individual fell hard, but not hard enough to break a bone, which explains why he was able to walk it off.