Mechanics Flashcards
Scalar quantity
A quantity that has only magnitude
Vector quantity
A quantity that has magnitude as well as direction
Is acceleration vector or scalar
Vector
Is mass scalar or vector
Scalar
Difference between mass and weight
Mass is scalar and is not dependent on the gravity acting upon it. Weight is a vector and depends on the gravitational field strength
W = mg
Equilibirum
¬ Sum of anticlockwise moments = sum of clockwise moments
¬ Stationary or moving at a constant velocity
How can forces acting on an object be shown in equilibrium
¬ Adding the horizontal and vertical components of the forces acting on it, showing they equal zero
¬ Or is there are 3 forces acting on it you can draw a scale diagram, if the scale diagram forms a closed triangle, then the object is in equilibrium
What is a moment
A turning force : force multiplied by the perpendicular distance from the point to the line of action of the force
Couple
A pair of equal and opposite coplanar forces
Centre of mass
The point through which all the mass of an object acts, for a uniform object the centre of mass is the centre of the object
Velocity
The change in displacement per unit time
Can be found by measuring the gradient of a tangent to a displacement time graph
Area under a velocity / acceleration time graph
The displacement travelled and the velocity respectively
A ball is projected off of a wall at 6m/s how does its horizontal velocity change from its launch until it hits the ground
The horizontal velocity remains the same as there is no acceleration in that direction
Vertical acceleration
The vertical acceleration is equal to the gravitational field strength
Terminal velocity
When forces acting on h falling object become balanced, the acceleration becomes zero and the object is moving at max velocity
Friction
A resistance to motion between an object and a surface or an object moving through a fluid. Friction is a force that acts in the opposite direction to the movement
Newton’s third law
Every force has an equal and opposite reaction
Newton’s second law
F=ma
Where mass is constant, F is the force applied and a is acceleration
Newton’s first law
An object stays moving at a constant velocity until a force acts upon it
Difference between elastic and inelastic collisions
Elastic = kinetic energy before is equal to the kinetic energy afterwards
Inelastic = kinetic energy at the end is not equal to the kinetic energy at the start
Momentum equation
momentum = mass x velocity
Is linear momentum only conserved in elastic collisions?
No, linear momentum is always conserved
Force definition
Rate of change of momentum
Impulse definition
Change in momentum
F(change in)t = (change in)mv
Area under force time graph
Impulse
Fs cos(0) = ?
The work done / energy transferred
What is rate of work done equal to
power
What is efficiency
Useful output power / input power
Principle of conservation of energy
Energy cannot be created or destroyed, only transferred into other forms of energy
Therefore the total every in a closed system will always remain the same
What is lift
An upward force which acts on objects travelling in a fluid, it is caused by the object creating a change in direction of fluid flow and acts perpendicular to the direction of fluid flow
