Mechanics Flashcards
What is instantaneous velocity?
It is the velocity at any given time, equal to the gradient of the tangent on a displacement time graph.
What quantities are used in SUVAT situations, and what are their units?
s = displacement (m) u = initial velocity (ms^-1) v = final velocity (ms^-1) a = constant acceleration (ms^-2) t = time taken (s)
What represents the following on a velocity time graph?
acceleration
displacement
- the gradient
- the area under the graph
What does a velocity time graph look like for a bouncing ball?
A /I/I/I shape alternating between -ve and +ve velocity, with (near) vertical lines representing changes in direction of velocity
How do you approach a two stage Suvat question?
Sketch a graph of v/t, and work out changes in gradient separately.
What is the acceleration of objects falling or decelerating vertically?
g - 9.81 ms^-2 . You can decide to view this as -ve or positive depending on what if you consider upwards as +ve.
Describe the velocity and motion of horizontal projection.
Horizontal and vertical motions and vertical motions are independent of each other, and together are parabolic.
Horizontal motion is constant velocity of uₓ = vₓ , a = 0.
Vertical motion is constant acceleration due to gravity.
These vectors can be resolved to find the final velocity v, and the angle.
Describe the velocity and motion of non-horizontal projection.
Horizontal and vertical motions and vertical motions are independent of each other, and together are parabolic.
The initial velocity, u, needs to be resolved into uₓ and uᵧ using trig.
Horizontal motion is constant velocity of uₓ = vₓ
Vertical motion is constant acceleration due to gravity.
How do you find the following from non-horizontal projection?
- The max. height reached
- The time of flight
- find sᵧ when vᵧ = 0
- find t when sᵧ = 0
What are the following terms?
- displacement
- velocity
- acceleration
- The distance moved in a particular direction.
- The rate of change of displacement
- When the motion of an object changes, either in velocity or direction.
What affects the drag force of fluid resistance? [3]
- The velocity of the object: F ∝ v
- The viscosity of the fluid
- The shape of the object
What is Newton’s First law?
- If there is no resultant force acting on an object, it will continue to move in uniform motion, or be at rest. In this case, the object is in equilibrium (no resultant force: ∑F = 0)
- A resultant force will cause acceleration.
What is Newton’s Second law?
- For a constant mass?
- In terms of momentum?
- The resultant force is proportional to the acceleration, with a constant mass. F = ma.
- The resultant force is equal to the rate of change of momentum. F = Δp / Δt
What is Newton’s Third law?
For every force exerted on an object, it will always exert an equal and opposite force on the other object.
What is a third law pair of forces?
- Forces that are the same size
- Forces that are in opposite directions
- Forces that act on different objects. Because of this, the forces do not have a resultant of 0.
- The same type of force.