Newtonian Mechanics and Forces

No force means no acceleration implying constant velocity. Also as velocity is constant kinetic energy remains constant. The angular momentum may change due to the change in moment of inertia. Also the total mechanical energy may change due the change in potential energy.

If we apply a torque on a body, then angular momentum of the body changes according to the relation
$\bar{\tau} = \displaystyle\frac{d\bar{L}}{dt} \Rightarrow if \space \bar{\tau} = 0$ then, $\overrightarrow{L} = constant$

Since no external torque act on gymnast, so angular momentum $(L =

I\omega)$ is conserved. After pulling her arms & legs, the angular velocity increases but moment of inertia of gymnast, decreases in, such a way that angular momentum remains constant.

The boy does not exert a torque to rotating table by jumping, so angular momentum is conserved i.e., 
$\displaystyle\frac{d\bar{L}}{dt} = 0 \Rightarrow \bar{L} = constant$

As the motion is circular, friction opposes the centripetal acceleration, thus its direction changes regularly.

Free fall occurs when gravity is the only force acting on an object, causing it to accelerate downward at the rate of gravity.

The Law of Universal Gravitation states that every particle of matter in the universe attracts every other particle with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them.

Gravity is a fundamental force of attraction that exists between all objects with mass. The strength of this force depends on the mass of the objects and the distance between them.

Air resistance is a fluid friction force that acts against the motion of an object moving through the air. Gravity and magnetism are not opposing forces in this context, and friction usually refers to surface contact.

In the absence of air resistance, gravity acts on all objects with the same acceleration. Therefore, a brick and a feather would fall at the same rate.

Gravity is strictly an attractive force; it pulls objects toward each other. It cannot push objects away.

Gravity is defined as the force of attraction between two objects that have mass. Inertia is an object's resistance to change in motion, and magnetism is a different force entirely.

As the piston of pump is pulled up, the pressure inside decrees which leads to unbalance of pressures.

Pressure is defined as Force divided by Area (P = F/A). Therefore, increasing the force or decreasing the area will increase the pressure.

The mechanical advantage (MA) of any machine, including a lever, is defined as the ratio of the load force overcome to the effort force applied. Therefore, it is expressed as load divided by effort.