Escape Velocity

In physics, escape velocity is the minimum speed needed for an object to "break free" from the gravitational attraction of a massive body. More particularly, escape velocity is the velocity (speed traveled away from the starting point) at which the sum of an object's kinetic energy and its gravitational potential energy is equal to zero. At escape velocity the object will move away forever from the massive body, without additional acceleration applied to the object. As the object moves away from the massive body, the object will continually slow and asymptotically approach zero speed as the object's distance approaches infinity.

For a spherically symmetric massive body such as a (non-rotating) star or planet, the escape velocity at a given distance is calculated by the formula

where G is the universal gravitational constant (G = 6.67×10⁻¹¹ m³ kg⁻¹ s⁻²), M the mass of the body to be escaped, and r the distance from the center of mass of the mass M to the object. Notice that the relation is independent of the mass of the object escaping the mass body M. Conversely, a body that falls under the force of gravitational attraction of mass M from infinity, starting with zero velocity, will strike the mass with a velocity equal to its escape velocity.

In this equation atmospheric friction (air drag) is not taken into account.

Source: Wikipedia

In hyperPhysics website you can input some data and it gives the escape velocity: http://hyperphysics.phy-astr.gsu.edu/hbase/vesc.html

See the escape velocity of Earth and Mars here: http://bit.ly/1iThICI

full computaion here http://wolfr.am/7ijFlEcl

Listen about escaping probes in this Astronomy Cast:

Ep. 384: Escaping Probes by Astronomy Cast on Mixcloud

Length vs Speed

I don't know who made this graphic, but it's a great way to compare length vs speed and the Physics that can be applied.

Not guilty!

The paper shows that if a car stops at a stop sign, an observer, e.g., a police officer, located at a certain

distance perpendicular to the car trajectory, must have an illusion that the car does not stop, if the

following three conditions are satis ed: (1) the observer measures not the linear but angular speed

of the car; (2) the car decelerates and subsequently accelerates relatively fast; and (3) there is a

short-time obstruction of the observer's view of the car by an external object, e.g., another car, at

the moment when both cars are near the stop sign.

Read the preprint paper in arXiv.org

Angry Birds Space: NASA announcement

Angry Birds is a good way to teach Physics. Topics like kinematics (motion, velocity, acceleration), dynamics (force, collisions), and energy are great to learn with that game.
Techradar website explores velocity and distance (post 1) and stretching and collisions (post 2);
wired website explores the elastic force, acceleration and analysis.http://www.wired.com/wiredscience/2011/11/physics-of-the-yellow-angry-bird/

Angry birds presentation

 

View more PowerPoint from linhvu28

Angry Birds Space is coming and NASA made "the announcement":

Measure the Speed of Light with Chocolate

"'C' is for chocolate! 'c' is also the symbol used for the speed of light. Defined as being 299,792,458 meters per second in vacuum, you can take a crack at measuring the ultimate speed using your microwave, a ruler and a bar of chocolate! Yum!" (Jefferson Lab - YouTube)

Well, lets see how they do it:

And now the calculations:

To calculate the speed of light, we can use the math's expression of speed:

v = Dx/Dt

In this case, Dx = l and Dt = T and T = 1/f (T is the period and f the frequency of the wave, and l the wavelength).
The holes that appear in the chocolate corresponds to the maximum and minimum in a steady wave. So the wavelength is two times this distance:
l = 2 x 7.1 cm = 2 x 7.1 x 10^-2 m
The frequency can be read in the back of your microwave. In this case, the value corresponds to f = 2 450 MHz = 2 450 x 10⁶ s^-1.


So, velocity is:
v = l x f <=> v= 2x(7.1 x 10^-2 m) x (2 450 x 10⁶ s^-1) = 3.48 x  10⁸ m s^-1 .


That brings a percent error:


e = |c - v|/|c| x 100 = | 2.99 x  10⁸ - 3.48 x  10⁸|/|2.99 x  10⁸| x 100 = 16 %

Breaking the speed of light?

Let's break the speed of light in your backyard :)