Mechanics Flashcards
What are scalar quantities?
Scalar quantities have magnitude only.
What are vector quantities?
Vector quantities have a magnitude and a direction.
Scalar or Vector?
- Distance
- Mass
- Velocity
- Energy
- Weight
- Acceleration
- Temperature
- Displacement
- Force
- Speed
- Scalar
- Scalar
- Vector
- Scalar
- Vector
- Vector
- Scalar
- Vector
- Vector
- Scalar
What should an appropriate scale look like?
An appropriate scale should maximise the amount of graph space available.
Calculating the final vector can be done in two ways:
- By measurement of the diagram, if it is drawn to scale
- By using Pythagoras/trigonometry
How would you work out the magnitude of a vector?
[Use the following question as an example]
A 3N northwards force and a 4N eastwards force act on a mass. What is the magnitude of the resultant force?
√3² + 4²
=√9 + 16
=√25
=5N
How would you work out the direction of a vector?
[Use the following question as an example]
A 3.0N northwards force and then a 4.0N eastwards force act on a mass. What is the direction of the resultant force?
- Draw Triangle.
(AB=3, BC=4) - Lable angle required.
(BAC) - Lable sides of the triangle with opposite-adjacent-hypotenuse.
- Choose the correct equation from SohCahToa.
(In this case Toa) - Write out the formula with know values.
(Tan(θ) = 4/3) - Rearrange and solve, giving the answer to an appropriate s.f
(Tan⁻¹(4/3) = θ, θ = 53⁰) - Write the answer in relation to the direction.
(53⁰ East from North/the verticle)
How would you resolve a vector?
- Sketch the vector.
- Lable sides of the triangle with opposite-adjacent-hypotenuse.
- Choose the correct equation from SohCahToa.
- Write out the formula with know values.
- Rearrange and solve, giving the answer to an appropriate s.f
- Repeat the same steps for the other axis.
What are the suvat quantities?
s: distance
u: initial velocity
v: final velocity
a: acceleration
t: time
What is instantaneous velocity?
Velocity at a given point
What is average velocity?
Can be found using (u + v)/2
if acceleration is constant
What is rectilinear motion?
Moving in a straight line.
What is the vertical acceleration due to gravity?
9.81ms⁻²
Displacement-time graphs:
What does the gradient show?
Velocity (not speed because a direction is shown)
Velocity-time graphs:
What does the gradient show?
What does the area under the graph show?
Gradient: Acceleration.
Area: Displacement.
What is newtons first law?
An object at rest will remain at rest…
An object in motion will remain in motion…
…unless acted on by an unbalenced force.
What is newtons second law?
The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.
What is newtons second law?
quantativly
∑F = ma
What is newtons third law?
Every action has an equal but opposite reaction.
Is momentum scalar or vector?
Vector.
How do you calculate momentum (p) given the mass and velocity of an object.
p = mv
What is the law of conservation of momentum?
The total momentum before must be the same as the total momentum after, because linear momentum is always conserved (provided no external force acts on the bodies).
How do you quantitivly show conserved momentum when the masses move off together?
mₜ₁vₜ₁ + mₜ₂ vₜ₂ = (mₜ₁ + mₜ₂) vₜ₁₂
How do you quantitivly show conserved momentum when the masses move off separately?
mₜ₁vₜ₁ + mₜ₂ vₜ₂ = mₜ₁vₛ₁ + mₜ₂ vₛ₂
