Mechanics Flashcards
Scalars
Describe only a magnitude.
Vectors
Describe magnitude and direction.
Example of scalars
Distance, speed, mass, temperature
Example of vectors
Displacement, velocity, force/weight, acceleration
When should scale drawings be used?
When vectors are at angles other than 90 degrees.
What must be happening for an object to be in equilibrium?
The sum of all forces acting on it must be zero.
Moment
Moment = Force X Perpendicular distance to line of action of force from the point
Couple
A couple is a pair of force within the same plane where the two forces are equal in magnitude but act in opposite directions.
Moment of a couple
Force X Perpendicular distance between the lines of action of forces.
Principle of moments
For an object in equilibrium, the sum of anticlockwise moments about a pivot is equal to the sum of clockwise moments.
Center of mass
The point at which an object’s mass acts.
Uniform
its centre of mass will be exactly at its center.
Speed
Scalar quantity which describes how quickly an object is travelling
Displacement
The overall distance travelled from the starting position.
Velocity
The rate of change of displacement.
Acceleration
The rate of change of velocity.
Instantaneous velocity
The velocity of an object at a specific point in time.
Average velocity.
The velocity of an object over a specified time frame.
Uniform acceleration
Where the acceleration of an object is constant.
Acceleration time graphs
Represent the change in velocity over time. The area under the graph is change in velocity.
Velocity time graphs
Represent the change in velocity over time. Therefore the gradient of a VT graph is acceleration. Area is displacement.
Displacement time graphs
Change in displacement over time, their gradient represents velocity.
Free fall
Where an object experiences an acceleration of g.
Friction
The force which opposes the motion of an object. They convert kinetic energy into other forms.
Magnitude of air resistance
Increases as the speed of the object increases.
Lift
An upwards force which acts on objects travelling in a fluid. Acts perpendicular to the direction of fluid flow.
Terminal speed
Occurs where the frictional forces acting on an object and driving forces are equal. No resultant force no acceleration. Object travels at a constant speed.
Skydiver terminal speed example
- As they leave the plane, they accelerate as their weight is greater than the air resistance.
- As the skydiver’s speed increases, the magnitude of air resistance also increases. This continues until the force of weight and air resistance become equal = terminal velocity is reached.
Air resistance
Affects both the vertical and horizontal components of a projectile’s motion.
Newton’s first law
An object will remain at rest or travelling at a constant velocity, until it experiences a resultant force.
Newton’s second law
The acceleration of an object is proportional to the resultant force experienced by an object. F=ma
Newton’s third law
For each force experienced by an object, the object exerts an equal and opposite force.
Free body diagram
A diagram which shows all the forces that act upon an object.
Momentum
The product of mass and velocity of an object.
What happens to momentum in any interaction?
Momentum is always conserved in any interaction where no external forces act.
Impulse
The change of momentum.
Elastic collision
Where both momentum and kinetic energy are conserved.
Inelastic collision
Where only momentum is conserved. While kinetic energy is converted into other forms.
Work done
The force causing a motion multiplied by the distance travelled in the direction of the force.
Power
The rate of energy transfer.
Where can you find the Work done if you can’t use the formula?
The area under a force-displacement graph.
Efficiency
The measure of how efficiently a system transfers energy. Calculated by dividing useful power output by total energy input.
Conservation of energy
Energy cannot be created or destroyed, but can be transferred from one form to another.
