4. Mechanics and Materials Flashcards
What is meant by a scalar quantity?
A quantity that has only magnitude.
What is a vector quantity?
A quantity that has magnitude as well asdirection.
Is acceleration a vector or scalar quantity?
Vector
Is mass a scalar or vector quantity?
Scalar
What is the 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
If an object is in equilibrium the sum of the anti clockwise moments would be …
Equal to the sum of the clockwise moments (principle of moments).
If an object is in equilibrium it means the object is …
Not accelerating, so is either:
● Stationary, or
● Moving at a constant velocity
How can the forces acting on a object be shown to be in equilibrium?
● Adding the horizontal and vertical components of the forces acting on it, showing they equal zero.
● Or if there are 3 forces acting on the object 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.
What is meant by a couple?
A pair of equal and opposite coplanar forces
What is meant by the 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
If you have a uniform object, where would its centre of mass be?
At the centre of the solid
What can be described as ‘the change in displacement per unit of time’?
Velocity, instantaneous velocity can be found by measuring the gradient of a tangent to a displacement-time graph
What is the area under a velocity-time and acceleration-time graph?
The displacement travelled and the velocity respectively
As speed increases, air resistance ….
Increases (proportional to the square of the speed)
A ball if projected off a castle 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.
How do the SUVAT equations reflect that that all objects fall at the same rate?
Mass is not included in the SUVAT equations, showing that the mass of an object does not affect its speed or acceleration.
In projectile motion, what is the vertical acceleration?
The vertical acceleration is equal to gravitational field strength (g).
What is meant by terminal velocity?
When the forces acting on the falling object become balanced, the acceleration becomes zero and the object is moving at maximum velocity.
What is meant by 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.
Which of Newton’s Laws state ‘every action force has an equal and opposite reaction force’?
Newton’s third law
What is Newton’s second law?
F = ma Where mass (m) is constant, F is the force applied and a is the acceleration.
What is Newton’s first law?
An object stays moving at a constant velocity until a force acts upon it.
What is the difference between elastic and inelastic collisions?
In an elastic collision the kinetic energy before is equal to the kinetic energy afterwards.
In an inelastic collision the kinetic energy at the end is not equal to the kinetic energy at the start.