3A2 Frames of Reference Flashcards
Identify the role of frames of reference in terms of their applications.
Define:
Frame of reference
It is a coordinate system used to measure positions, velocities, and accelerations of objects.
Different frames can yield different observations of motion.
True or false:
A reference frame must always be stationary.
False
A reference frame can be stationary or in motion, depending on the observer’s perspective. Motion is described relative to a chosen reference frame.
Fill in the blank:
A reference frame that is not accelerating is called an _______.
intertial frame of reference
Newton’s laws apply directly in inertial frames.
How is an inertial frame of reference related to the law of inertia?
The law of inertia states that objects in an inertial frame of reference remain at rest or move at a constant velocity unless acted upon by an external force.
Inertial frames are critical for understanding Newtonian mechanics.
Why is the concept of a frame of reference necessary in describing motion in space?
In space, where there is no fixed background, observations vary based on the chosen reference.
Frame of reference, such as the spacecraft or a celestial body.
Compare an inertial and a non-inertial frame of reference.
An inertial frame moves at constant velocity (no acceleration); a non-inertial frame accelerates and requires fictitious forces.
Examples of non-inertial frames include rotating or accelerating systems.
Define:
Fictitious forces
Apparent force observed in a non-inertial frame of reference, arising due to the acceleration of the frame itself.
Fictional forces are perceived effects of the law of inertia in non-inertial frames, not actual forces. Examples include the sensation of being pushed forward in a car when brakes are applied.
Why do fictitious forces contradict Newton’s third law?
Because they do not result from a physical interaction between two objects and, therefore, lack an equal and opposite reaction force.
Newton’s third law applies to forces arising from interactions, while fictitious forces are apparent effects in non-inertial frames.
True or false:
Fictitious forces are needed in an inertial frame.
False
Only non-inertial frames require fictitious forces; Newton’s laws work normally in inertial frames.
Fill in the blank:
A train pulling away from a platform is an example of a ____-______ frame of reference.
non-inertial
This is because the train is accelerating, causing apparent changes in motion of objects.
Fill in the blank:
The apparent force experienced in a rotating reference frame is called _____ _____.
centrifugal force
Centrifugal force is a fictitious force observed in non-inertial frames
Why is Earth often treated as an inertial frame of reference?
For most practical applications, Earth’s rotation and revolution have negligible effects on observed motion.
Ignoring rotation makes motion calculations easier.
In a rotating reference frame, an object appears to deflect to the right in the Northern Hemisphere. Which fictional force explains this?
The Coriolis force
The Coriolis effect is crucial for weather patterns and ocean currents.
What fictitious force is felt by a person in an elevator accelerating upwards?
A downward force making you feel heavier.
This is due to the non-inertial frame of reference inside the accelerating elevator.
What fictitious force does a passenger feel in a suddenly accelerating car, and in which direction?
A backward force, making it feel like you’re being pushed into the seat.
This apparent force is due to the car being a non-inertial frame of reference during acceleration.
A ball is thrown inside a moving train. Why might its motion appear curved to an observer outside but straight to an observer inside?
Different frames of reference change how motion is perceived due to relative velocity.
Motion depends on the observer’s frame (train or ground).
Define:
Coordinate system
Mathematical framework used to define the position of points in space. It provides a reference for measuring motion relative to a specific frame of reference.
Common coordinate systems include Cartesian (x, y, z), Polar (r, θ), Spherical (r, θ, φ).
Provide an example of a coordinate system used as a frame of reference.
A Cartesian coordinate system with axes aligned to a laboratory setup.
It simplifies measuring positions and velocities.
Why are Cartesian coordinates often used to analyze motion in a frame of reference?
Position is described using x, y, and z axes relative to the chosen origin, and are ideal for problems involving inertial frames and linear trajectories.
They simplify calculations for straight-line motion.
Fill in the blank:
Polar coordinates are useful for describing motion in _______ or rotational systems.
circular
In polar coordinates, a point is defined by its distance from a reference point (radius) and an angle from a reference direction.
When are spherical coordinates most useful?
Problems involving three-dimensional motion, such as describing the position of celestial bodies in astronomy.
Uses radius (r), polar angle (θ), and azimuthal angle (φ).
How does the choice of a coordinate system affect calculations in different frames of reference?
The coordinate system aligns with the symmetry of the problem, simplifying equations of motion and transformations between frames (e.g., rotating frames).
For example, using polar coordinates in a rotating non-inertial frame simplifies understanding fictitious forces.
Define:
Relative motion
It is the motion of an object as observed from a particular frame of reference, which may itself be in motion.
The description of an object’s motion can differ between observers depending on their frame of reference.
True or false:
Relative motion can differ based on the chosen frame of reference.
True
For example, a stationary observer on the ground sees a ball thrown in a moving train differently than a passenger inside the train.
Define:
Relative velocity
The velocity measured with respect to a given observer from a specific frame of reference.
It depends on the motion of both the object and the observer.
True or false:
Relative velocity is always the same for all observers.
False
It varies depending on the observer’s frame of reference. Motion is relative to the observer.
Why does the Moon seems stationary to an astronaut on its surface?
The astronaut shares the Moon’s frame of reference, so there is no observed motion.
Motion is relative to the chosen frame.
What is the formula to find the relative velocity of two objects with respect to an external frame?
Vac = Vab + Vbc
Vac represents the velocity of object “a” with respect to reference frame “c”.
Vab represents the velocity of object “a” with respect to reference frame “b”.
Vbc represents the velocity of object “b” with respect to reference frame “c”.
If a plane flies north at 500 mph and a man in the plane flies north at 15 mph, what is the relative velocity of the man with respect to the ground?
515 mph
Relative velocity: Vrel = Vplane + Vman (same direction).
Fill in the blank:
The formula for relative velocity is ______.
Vrel= Vb - Va
Vrel is relative velocity.
Vb and Va are the velocities of two objects relative to a chosen frame.
A car moves at 80 mph toward a man running west at 10 mph. What is the relative velocity?
-90 mph
The negative indicates the direction of the car’s movement relative to the man.
