Unit 4 Mechanics Flashcards
Define scalar and vector quantities.
Scalar quantities have magnitude only and vector quantities have magnitude and direction
What is an object at equilibrium?
Object at rest or moving with a constant velocity
State the conditions for an object to be in equilibrium
The resultant force on it must be zero.
The total clockwise moment about any point on the object must equal the total anticlockwise moment about that point
Define the moment of a force about a point
Moment = force x perpendicular distance from the point to the line of action of the force
Define the moment of a couple
Force x perpendicular distance between the lines of actions of the forces
What does the principle of moments state?
Sum of clockwise moments about any point = sum of anticlockwise moments about that point
Define centre of mass.
The point through which a single force has no turning effect when applied - it is the point at which the weight of a body acts. An object will topple over if the line of action of its weight is outside of its base.
How is steady speed represented on a displacement time graph?
Straight line with a constant gradient
What does a curved line on a velocity time graph represent?
Changing acceleration
What does a value of zero on an object’s acceleration - time graph indicate?
Object is moving with constant velocity
What are the conditions for an object to be in free fall?
Only has its weight (force of gravity) acting on it
Give the properties for the motion of a projectile
Acceleration is due to gravity, is always acting downwards, and only affects the vertical motion of the object
Horizontal velocity is always constant because there is no horizontal force or acceleration
What happens to the trajectory of a projectile if air resistance acts on it?
Downward trajectory will be steeper than upward trajectory
Its horizontal speed, range and maximum height will be reduced
State properties of drag (frictional forces)
Acts in the opposite direction to an object’s movement
Increases with increasing viscosity of a fluid
Increases with increasing speed of an object
Dependant on the shape and size of the object
Causes a moving object to slow down and stop if there is no force propelling it
Define inertia
Inertia is the tendency of objects in motion to stay in motion, and objects at rest to stay at rest
State Newton’s first law of motion
Velocity of an object will only change is a resultant force is acting on it
State Newton’s second law of motion
Acceleration of an object is proportional to the resultant force on the object and inversely proportional to the mass of the object
What are the properties of a pair of forces related by Newton’s third law?
Same size
Act on separate objects
Act in opposite directions
Along the same line
Same type
What happens in an elastic collision?
Kinetic energy is conserved - the objects involved will have the same kinetic energy after the collision as before
What happens in an inelastic collision?
Kinetic energy is not conserved - the objects involved will have less kinetic energy after the collision than before
What is the principle of conservation of momentum?
Total momentum before two objects collide = total momentum after they collide
State Newton’s second law in terms of momentum
Force acting on an object is equal to rate of change of momentum of the object
State the relationship between impulse and momentum
Impulse = change of momentum
What does the area under the line of a force time graph represent?
Impulse of the force or object change in momentum
How do many everyday safety features reduce the force of an impact?
Increase time taken for, a change in momentum, reducing impact force
Define power
Rate of energy transfer or rate of doing work
Power = force x velocity
Define efficiency
Measure of how much energy is wasted in an energy transfer
State the principle of conservation of energy
Energy cannot be created or destroyed, only transferred between different stores and objects
