4.1 - Mechanics

• What is meant by a scalar quantity?

  A quantity that only has magnitude
• What is a vector quantity?

  A quantity that has both magnitude and direction
• 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 anti-clockwise moments would be...

  Equal to the sum of clockwise moments (principle of moments)
• If an object is in equilibrium, it means that the object is...

  Not accelerating, so either staying at the same velocity or stationary
• How can the forces in an object be shown to be in equilibrium?


  - Adding the horizontal and vertical components of the forces acting on it, showing that they are zero

  - Or if there are three 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 graph?

  The displacement travelled
• As speed increases, air resistance...

  Increases (proportional to the square of speed)
• A ball is projected off a castle at 6ms^-1, 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 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?

  Gravitational Field Strength (9.81ms^2 for physics unless stated otherwise)
• 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 that every action force has an equal and opposite force?

  Newton's third law
• What is Newton's second law?

  Force = mass x acceleration (F=ma)
• What is Newton's first law?

  An object will remain stationary or maintain the same velocity unless there is a resultant force acting on it
• What is the difference between elastic and inelastic collisions?

  In an elastic collision, kinetic energy is conserved.

  
  

  In an inelastic collision, kinetic energy is not conserved.
• The rate of change of momentum can be described as?

  Force
• What is impulse?


  The change in momentum
• What does the area under a force-time graph represent?

  Impulse
• What is the rate of work done equal to?

  Power
• What is efficiency?


  Efficiency = Useful Output / Total Input
• What is meant by the principle of conservation of energy?

  Energy cannot be created or destroyed, only transferred into other forms of energy
• What is lift?


  An upwards 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.