Topic 2 (again) Mechanics Flashcards
What is a scalar quantity?
Quantity with magnitude only, no direction
What is a vector quantity?
A quantity with magnitude and direction
What are the two methods to find the resultant vector?
- Trigonometry
- Scale diagram
Define speed.
how far something is moving, regardless of direction
Define displacement.
How far an object has traveled from its starting position
define velocity.
The rate of change of an objects displacement
what is instantaneous speed?
the speed of an object at any given time
what must suvat equations have for them to work?
constant acceleration
what is the force on an object due to gravity called?
weight
what is g?
gravitational field strength / acceleration due to gravity and its equal to 9.81
How do you calculate projectile motion of objects?
Resolve the initial velocity into horizontal and vertical components
Why would videoing a projectile be useful?
- You can plot its course by recording its position in each frame
- You can work out the velocity if you know the frame rate
Name a method of invesitgating projectiles?
Strobe photography, needs a reference object
What can you learn from a displacement-time graph?
- The gradient is the velocity
- If you have a curve, the object is accelerating
How do you find instantaneous velocity from a displacement-time graph?
Draw a tangent to the curve at the given time then calculate the gradient of the tangent
What can you learn from a velocity-time graph?
- The gradient is the acceleration
- Area under the graph is the displacement
What are free-body diagrams?
Diagrams that show all the forces acting on a body
How can you find the resultant force if two forces are acting on an object?
Draw them “tip-to-tail” and then use trigonometry to calculate the angle and length
What does newtons first law say?
if there is no resultant force on an object, the object will remain at constant velocity or rest (the velocity will not change)
What does newtons second law state?
If there is a resultant force acting on an object, the object will accelerate.
This acceleration is proportional to the magnitude of the force
F = ma
What does newtons third law say?
Each force has an equal and opposite reaction force
Explain newtons third law
If object A exerts a force on B, then B will exert an equal but opposite force on A
Define friction
A force that opposes motion
What direction do frictional forces always act in?
in the opposite direction to the motion of an object
What do frictional forces always do?
- slow something down
- convert kinetic energy into heat or sound
What conditions does there need to be for an object to reach terminal velocity?
- A driving force that stays the same
- A frictional force that increases with velocity
Why might a skydiver reach multiple terminal velocities in the same jump?
- Reaches one without parachute open
- Open parachute and then reaches another, just a far slower terminal velocity
How do you calculate momentum?
momentum = mass x velocity
What is always true about momentum?
- It is always conserved
What units is momentum measured in?
kgms^-1
If you divide momentum by time, what do you get?
Force
Define work done,
Energy transferred
how do you calculate work done?
W=fx
Work done = force x distance moved
How is work done different to total energy?
Its just the energy transferred, doesnt include all the energy that stays in their stores
What must be true about the direction to use w=fs?
The direction of the force is the same as the direction of motion
define power.
the rate of doing work
How do you calculate power?
Power = work done / time
P=w/t
What is the conservation of energy?
Energy cant be created or destroyed, only transferred
how do you calculate kinetic energy?
Ek = 1/2 m v^2
How is GPE calculated?
mgh
mass x gravitational field strength x height
how is energy “lost”?
it is dissipated to useless energy stores
What is efficiency?
How well a device converts the energy put in into useful energy out
How do you calculate effiiciency?
Useful energy input / total energy output x 100
Can be power instead of energy
Define mass
The amount of matter an object has
How do you calculate weight?
w = mg
mass x gravitational field strength
Define centre of gravity?
The single point through which an object’s weight can be considered to act
What is a moment?
The turning affect of a force
How do you calculate a moment?
M = Fx
Force x Perpendicular distance from pivot
What must be true for an object to be in equlibrium?
- Forces must be balanced
- net moment must be zero
