Physics and Human Affairs: Motion and Relativity (Week 1–2)

A set of Q&A flashcards covering motion, measurement methods, and basics of relativity based on the lecture notes.

What is motion?

Motion is a change in an object's position relative to a given reference or observer during a certain time interval; without identifying the observer, you can't say whether the object moved.

What is a dot diagram?

A diagram that shows an object's position at successive equal time intervals using dots to illustrate the path of motion.

What is a motion diagram?

A diagram that uses arrows to represent an object's velocity at successive moments, conveying direction and relative speed.

What is speed?

Speed is how fast an object is moving; it is distance divided by time and is a scalar quantity.

What is velocity?

Velocity is speed with a specified direction; it is a vector quantity.

What is acceleration?

Acceleration is the rate at which an object's velocity (speed with direction) changes over time.

What does the slope of a speed-time graph represent?

The slope represents acceleration; a horizontal slope means constant speed (zero acceleration).

What is the Principle of Relativity?

There is no experiment you can perform in a uniformly moving reference frame to determine that frame's absolute motion.

What does the constancy of the speed of light mean?

The speed of light in vacuum is the same for all observers, regardless of the motion of the light source or observer.

What is time dilation?

Time dilation is the effect where moving clocks run slower as observed from a stationary frame, increasing with speed.

What is length contraction?

Length contraction is the shortening of moving objects in the direction of motion as measured by an observer, relative to rest length.

What is relativistic mass?

Mass increases with speed as viewed from an outside frame, reflecting greater resistance to acceleration at high speeds.

What is the Law of Inertia (Newton's First Law)?

An object at rest stays at rest and an object in motion stays in motion at a constant speed in a straight line unless a nonzero net force acts on it.

What is net force?

The sum of all forces acting on an object; it determines whether and how the object's motion changes.

What are balanced forces?

Forces that cancel out so the net force is zero; typically no change in motion.

What are unbalanced forces?

Forces that do not cancel; the net force is not zero and the object's motion changes (accelerates).

What is a force diagram?

A sketch showing all forces acting on an object with arrows indicating direction and magnitude, along with a motion arrow for the object's movement.

What is the connection between force and motion?

Forces cause changes in motion; with no net force, motion remains constant.

What are inertial frames in Special Relativity?

Frames moving at constant velocity relative to each other; physics laws (and experiments) yield the same results in all inertial frames.

What is Special Relativity?

A theory describing physics in inertial frames moving at constant velocity, introducing time dilation, length contraction, and mass change with motion; E=mc^2 emerges from it.

What is General Relativity?

An extension of relativity that includes acceleration and gravity, describing curved spacetime and phenomena like black holes.

What is space-time?

The four-dimensional continuum combining three spatial dimensions and one time dimension in which events occur.

What does E=mc^2 signify?

Mass-energy equivalence: energy equals mass times the speed of light squared; mass and energy are interchangeable.

What is time?

Time is what clocks measure; clocks keep time by repeating a regular process at a constant rhythm.

What is a reference frame?

A coordinate system or observer used to describe motion; motion is relative to the chosen reference frame.

What is the difference between speed and velocity?

Speed is how fast an object moves (magnitude only); velocity includes both speed and direction.

How does a speed-time graph indicate acceleration?

A nonzero slope indicates acceleration; the steeper the slope, the greater the acceleration.

What happens to time and length at high speeds close to the speed of light?

Time dilates (slows down) and lengths contract (shorten) in the direction of motion as observed from a stationary frame.

What is motion?

Motion is a change in an object's position relative to a given reference or observer during a certain time interval; without identifying the observer, you can't say whether the object moved.

What is a dot diagram?

A diagram that shows an object's position at successive equal time intervals using dots to illustrate the path of motion.

What is a motion diagram?

A diagram that uses arrows to represent an object's velocity at successive moments, conveying direction and relative speed.

What is speed?

Speed is how fast an object is moving; it is distance divided by time and is a scalar quantity.

What is velocity?

Velocity is speed with a specified direction; it is a vector quantity.

What is acceleration?

Acceleration is the rate at which an object's velocity (speed with direction) changes over time.

What does the slope of a speed-time graph represent?

The slope represents acceleration; a horizontal slope means constant speed (zero acceleration).

What is the Principle of Relativity?

There is no experiment you can perform in a uniformly moving reference frame to determine that frame's absolute motion.

What does the constancy of the speed of light mean?

The speed of light in vacuum is the same for all observers, regardless of the motion of the light source or observer.

What is time dilation?

Time dilation is the effect where moving clocks run slower as observed from a stationary frame, increasing with speed.

What is length contraction?

Length contraction is the shortening of moving objects in the direction of motion as measured by an observer, relative to rest length.

What is relativistic mass?

Mass increases with speed as viewed from an outside frame, reflecting greater resistance to acceleration at high speeds.

What is the Law of Inertia (Newton's First Law)?

An object at rest stays at rest and an object in motion stays in motion at a constant speed in a straight line unless a nonzero net force acts on it.

What is net force?

The sum of all forces acting on an object; it determines whether and how the object's motion changes.

What are balanced forces?

Forces that cancel out so the net force is zero; typically no change in motion.

What are unbalanced forces?

Forces that do not cancel; the net force is not zero and the object's motion changes (accelerates).

What is a force diagram?

A sketch showing all forces acting on an object with arrows indicating direction and magnitude, along with a motion arrow for the object's movement.

What is the connection between force and motion?

Forces cause changes in motion; with no net force, motion remains constant.

What are inertial frames in Special Relativity?

Frames moving at constant velocity relative to each other; physics laws (and experiments) yield the same results in all inertial frames.

What is Special Relativity?

A theory describing physics in inertial frames moving at constant velocity, introducing time dilation, length contraction, and mass change with motion; E=mc^2 emerges from it.

What is General Relativity?

An extension of relativity that includes acceleration and gravity, describing curved spacetime and phenomena like black holes.

What is space-time?

The four-dimensional continuum combining three spatial dimensions and one time dimension in which events occur.

What does E=mc^2 signify?

Mass-energy equivalence: energy equals mass times the speed of light squared; mass and energy are interchangeable.

What is time?

Time is what clocks measure; clocks keep time by repeating a regular process at a constant rhythm.

What is a reference frame?

A coordinate system or observer used to describe motion; motion is relative to the chosen reference frame.

What is the difference between speed and velocity?

Speed is how fast an object moves (magnitude only); velocity includes both speed and direction.

How does a speed-time graph indicate acceleration?

A nonzero slope indicates acceleration; the steeper the slope, the greater the acceleration.

What happens to time and length at high speeds close to the speed of light?

Time dilates (slows down) and lengths contract (shorten) in the direction of motion as observed from a stationary frame.

What is Newton's Second Law of Motion?

Newton's Second Law states that the acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass, commonly expressed as \vec{F} = m\vec{a}.

What is Newton's Third Law of Motion?

For every action, there is an equal and opposite reaction; forces always occur in pairs.

What is mass?

Mass is a measure of an object's inertia, or its resistance to changes in motion; it is a scalar quantity.

What is weight?

Weight is the force of gravitational attraction on an object, which depends on its mass and the gravitational field it is in. It is a vector quantity, usually directed downwards.

What is inertia?

Inertia is the property of an object to resist any change in its state of motion; an object at rest tends to stay at rest, and an object in motion tends to stay in motion with the same velocity.