Mechanics Flashcards
(54 cards)
What is the difference between a scalar and a vector quantity?
Scalars have magnitude only (e.g., mass, speed), while vectors have both magnitude and direction (e.g., force, velocity).
Define distance and displacement. Which is scalar and which is vector?
- Distance: total path length traveled (scalar)
- Displacement: shortest straight-line distance between start and end point including direction (vector)
How do speed and velocity differ?
Speed is distance/time without direction (scalar), velocity is displacement/time including direction (vector).
Give three examples of scalar quantities and three examples of vector quantities.
- Scalars: mass, speed, temperature
- Vectors: force, velocity, acceleration
What is the resultant vector?
The single vector that has the same effect as two or more combined vectors (also called the net vector).
Describe how to add two vectors that are not perpendicular using a scale drawing.
1) Draw vectors head-to-tail using a suitable scale
2) Draw the resultant vector from the tail of the first to the head of the last
3) Measure length (magnitude) with a ruler and angle (direction) with a protractor
4) Convert measurements back to original units using the scale
How do you calculate horizontal and vertical components of a vector
F at angle θ?
Horizontal 𝐹𝑥=𝐹cosθ
Vertical 𝐹𝑦=𝐹sinθ
What is a moment in physics?
The turning effect of a force about a pivot point.
Write the formula for calculating a moment.
Moment (N·m) = Force (N) × Perpendicular distance from the pivot (m)
What is the SI unit of a moment?
Newton metre (N·m)
What does the Principle of Moments state?
For an object in equilibrium, the sum of clockwise moments about a pivot equals the sum of anticlockwise moments about the same pivot.
What is a couple?
A pair of equal and opposite coplanar forces that produce rotation only.
What are the characteristics of the forces in a couple?
- Equal in magnitude
- Opposite in direction
- Perpendicular to the distance between them
Does a couple produce a resultant force?
No, the resultant force is zero, so there is no linear acceleration.
Why does a couple produce rotation without translation?
Because the forces are equal, opposite, and separated by a distance, creating a turning effect without net force.
Write the formula for the moment of a couple.
Moment of a couple = Force × Perpendicular distance between the forces
What is the SI unit of the moment of a couple?
Newton metre (N·m)
What is the centre of mass of an object?
The point at which the weight of the object may be considered to act.
What is the difference between centre of mass and centre of gravity?
- Centre of mass does not depend on the gravitational field.
- Centre of gravity does depend on the gravitational field and may differ in non-uniform fields.
Define velocity.
The rate of change of displacement.
Define acceleration.
the rate of change of velocity.
Define instantaneous velocity.
Velocity at a specific point in time, found from the gradient of a tangent on a displacement-time graph.
Define average velocity.
Total displacement ÷ total time.
What does the gradient of a displacement-time graph represent?
Velocity.
