Let's play @home

During this days we can play with our children to try to build something like this:




Or you can create an easy one by using cardboard (image source: https://www.hellowonderful.co/post/15-impressive-ways-to-make-a-marble-run/)


Or like this one (image source: https://www.edenproject.com/learn/for-everyone/how-to-make-a-recycled-marble-run)


Let's be creative!

Galileo's Birthday

Today we celebrate Galileo's birthday (14 February 1564).

His contributions to observational astronomy include the telescopic confirmation of the phases of Venus, the discovery of the four largest satellites of Jupiter, and the observation and analysis of sunspots.

Galileo made original contributions to the science of motion by showing a remarkably modern appreciation for the proper relationship between mathematics, theoretical physics, and experimental physics. 

A biography by Galileo's pupil Vincenzo Viviani stated that Galileo had dropped balls of the same material, but different masses, from the Leaning Tower of Pisa to demonstrate that their time of descent was independent of their mass.Galileo proposed that a falling body would fall with a uniform acceleration, as long as the resistance of the medium through which it was falling remained negligible, or in the limiting case of its falling through a vacuum. He also derived the correct kinematical law for the distance travelled during a uniform acceleration starting from rest—namely, that it is proportional to the square of the elapsed time ( d ∝ t ² ). Prior to Galileo, Nicole Oresme, in the 14th century, had derived the times-squared law for uniformly accelerated change, and Domingo de Soto had suggested in the 16th century that bodies falling through a homogeneous medium would be uniformly accelerated. Galileo expressed the time-squared law using geometrical constructions and mathematically precise words, adhering to the standards of the day. (It remained for others to re-express the law in algebraic terms).

He also concluded that objects retain their velocity unless a force—often friction—acts upon them, refuting the generally accepted Aristotelian hypothesis that objects "naturally" slow down and stop unless a force acts upon them. Galileo was the first to express it mathematically, verify it experimentally, and introduce the idea of frictional force, the key breakthrough in validating the concept. Galileo's Principle of Inertia stated: "A body moving on a level surface will continue in the same direction at constant speed unless disturbed." This principle was incorporated into Newton's laws of motion (first law). (adapted from Wikipedia)

More info: 
http://galileoandeinstein.physics.virginia.edu/lectures/gal_accn96.htm
http://csep10.phys.utk.edu/astr161/lect/history/galileo.html

Look at the Sun

The science behind observing our star

The governing laws

The motion of objects is governed by Newton's laws. The same simple laws that govern the motion of objects on earth also extend to the motion of planets, moons, and other satellites. The mathematics that describes a satellite's motion is the same mathematics presented for circular motion described here.

So, the velocity, acceleration and ratio between period and radius can be acquired.

The period, speed and acceleration of a satellite are only dependent upon the radius of orbit and the mass of the central body that the satellite is orbiting.

The Lagrangian points [1]

The Lagrangian points are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects (such as a satellite with respect to the Earth and Moon). The Lagrange points mark positions where the combined gravitational pull of the two large masses provides precisely the centripetal force required to rotate with them.

Lagrangian points are the stationary solutions of the circular restricted three-body problem. For example, given two massive bodies in circular orbits around their common center of mass, there are five positions in space where a third body, of comparatively negligible mass, could be placed so as to maintain its position relative to the two massive bodies. As seen in a rotating reference frame with the same period as the two co-orbiting bodies, the gravitational fields of two massive bodies combined with the satellite's circular motion are in balance at the Lagrangian points, allowing the third body to be stationary with respect to the first two bodies.

There is an individual description of lagrangian points in ESA website. 

STEREO and SOHO

Two of the most important satellites that are observing our Sun is STEREO and SOHO

STEREO (Solar TErrestrial RElations Observatory) is the third mission in NASA's Solar Terrestrial Probes program (STP). The mission, launched in October 2006, has provided a unique and revolutionary view of the Sun-Earth System. The two nearly identical observatories - one ahead of Earth in its orbit, the other trailing behind - have traced the flow of energy and matter from the Sun to Earth. STEREO has revealed the 3D structure of coronal mass ejections; violent eruptions of matter from the sun that can disrupt satellites and power grids, and help us understand why they happen. STEREO is a key addition to the fleet of space weather detection satellites by providing more accurate alerts for the arrival time of Earth-directed solar ejections with its unique side-viewing perspective. (NASA)

SOHO, the Solar & Heliospheric Observatory, is a project of international collaboration between ESA and NASA to study the Sun from its deep core to the outer corona and the solar wind. (NASA)

Now lets watch trajectories and lagrange points in action [2]:

[1] text from wikipedia: http://en.wikipedia.org/wiki/Lagrangian_point (May 11, 2012)
[2] video shared by my friend Manel Rosa Martins.

Earth is slowing down rotation

Read more in this post.

Kepler's Birthday

Johannes Kepler (December 27, 1571 – November 15, 1630) is not a name that most people recognize, but if you are aware of the recent discoveries of new planets, will recognize that many new planets bear his name.  Perhaps the best birthday gift we can give to this scientist is Kepler 22b, the first planet discovered in the habitable zone of a star, an earth possible planet like ours.

Kepler is best known for revealing the secrets of planetary motions. His three laws of planetary motion still apply today, and enabled Newton to give us the law of universal gravitation.
In 1596, Kepler published Mysterium Cosmographicum, where he set out arguments for the heliocentric hypothesis.
In 1609 published Astronomia Nova ... From Motibus Stellae Martis, where he presented his three laws of planetary motion that now bear his name:

• The planets describe elliptical orbits with the sun at one focus.
• The radius vector connecting the planet to the sun describes equal areas in equal times. (law of areas)
• The squares of the periods of revolution (T) are proportional to the cubes of mean distances (a) from the Sun to the planets. T² = k a³, where k is a proportionality constant.

Probably most of us will never use this information in our life, but it does well to remember that those was important intellectual achievements of Western civilization. We could even think to remember Kepler itself and its laws would be enough, but Kepler had more projects, for example, projects of the first glasses for myopia and hyperopia.

Using modellus to study circular motion

Using the software modellus to study circular motion:

Using Modellus to Study Projectiles

Using the software MODELLUS to learn the Physics Laws of movement in a projectile motion:

Fireworks' Physics

Weekend Diversion: The Physics of Fireworks!

The way you launch a firework is basically the same way you launch a cannonball out of a cannon! You put a "lift charge" in between the actual firework and the bottom of a strong, closed tube/pipe, and ignite it, propelling the firework up.

How high you want it to go is dependent only on the initial velocity of your firework, which is almost always larger for bigger fireworks

Read the entire article by Ethan Siegel in: startswithabang