Velocity of one object as seen from another, found by vector subtraction.
The velocity of A relative to B is v_A/B=v_A-v_B. In rotating frames additional Coriolis and centripetal terms appear. Used for aircraft in wind, boats crossing rivers and mechanisms.
A plane heading east at 200 km/h with a 50 km/h north wind has a ground speed of 206 km/h.
Relative motion explains why two moving objects appear to move differently, which matters for vehicles, aircraft and moving frames.
Velocity of one object as seen from another, found by vector subtraction.
Relative motion explains why two moving objects appear to move differently, which matters for vehicles, aircraft and moving frames.
Subtract the velocity of the reference body from the velocity of the object you are interested in, using vectors.
Collisions depend on relative velocity along the line of impact, not on either body's velocity relative to the ground alone.
Typical applications include computing the velocity of a passenger relative to the ground on a moving train, finding the wind speed an aircraft must correct for to hold a course and planning the approach speed of two ships on a crossing course.
Study "Projectile motion" first (topic 23 of 106 in Engineering Mechanics). It covers the groundwork this topic builds on.
Relative velocity by vector subtraction. Closing speed in collisions. Choose a convenient reference frame.
A plane heading east at 200 km/h with a 50 km/h north wind has a ground speed of 206 km/h.
The next topic is "Curvilinear motion", which builds directly on this one.
It is classed as Beginner in Engineering Mechanics (topic 24 of 106). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.
Want to practise? Open the interactive course for quick checks, quizzes, simulations and progress tracking.