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  2. Eötvös experiment - Wikipedia

    en.wikipedia.org/wiki/Eötvös_experiment

    In 1889 he used the device with different types of sample materials to see if there was any change in gravitational force due to materials. This experiment proved that no such change could be measured, to a claimed accuracy of 1 in 20 million. In 1890 he published these results, as well as a measurement of the mass of Gellért Hill in Budapest. [3]

  3. Cavendish experiment - Wikipedia

    en.wikipedia.org/wiki/Cavendish_experiment

    The arm rotated until it reached an angle where the twisting force of the wire balanced the combined gravitational force of attraction between the large and small lead spheres. By measuring the angle of the rod and knowing the twisting force ( torque ) of the wire for a given angle, Cavendish was able to determine the force between the pairs of ...

  4. Fictitious force - Wikipedia

    en.wikipedia.org/wiki/Fictitious_force

    A fictitious force is a force that appears to act on a mass whose motion is described using a non-inertial frame of reference, such as a linearly accelerating or rotating reference frame. [1] Fictitious forces are invoked to maintain the validity and thus use of Newton's second law of motion, in frames of reference which are not inertial. [2]

  5. List of unsolved problems in physics - Wikipedia

    en.wikipedia.org/wiki/List_of_unsolved_problems...

    The following is a list of notable unsolved problems grouped into broad areas of physics. [1]Some of the major unsolved problems in physics are theoretical, meaning that existing theories seem incapable of explaining a certain observed phenomenon or experimental result.

  6. Hierarchy problem - Wikipedia

    en.wikipedia.org/wiki/Hierarchy_problem

    In theoretical physics, the hierarchy problem is the problem concerning the large discrepancy between aspects of the weak force and gravity. [1] There is no scientific consensus on why, for example, the weak force is 10 24 times stronger than gravity .

  7. Newton's laws of motion - Wikipedia

    en.wikipedia.org/wiki/Newton's_laws_of_motion

    In the absence of a net external force, the center of mass moves at a constant speed in a straight line. This applies, for example, to a collision between two bodies. [52] If the total external force is not zero, then the center of mass changes velocity as though it were a point body of mass . This follows from the fact that the internal forces ...

  8. Variable-mass system - Wikipedia

    en.wikipedia.org/wiki/Variable-mass_system

    At instant 1, a mass dm with velocity u is about to collide with the main body of mass m and velocity v. After a time dt, at instant 2, both particles move as one body with velocity v + dv. The following derivation is for a body that is gaining mass . A body of time-varying mass m moves at a velocity v at an initial time t.

  9. 21 grams experiment - Wikipedia

    en.wikipedia.org/wiki/21_grams_experiment

    The 21 grams experiment refers to a study published in 1907 by Duncan MacDougall, a physician from Haverhill, Massachusetts. MacDougall hypothesized that souls have physical weight, and attempted to measure the mass lost by a human when the soul departed the body. MacDougall attempted to measure the mass change of six patients at the moment of ...