Mechanics 1 Flashcards
Acceleration, momentum and weight are examples of what type of quantity?
Vector
Draw the vector diagram showing a stationary object on a flat desk
Weight acting down, equal and opposite reaction force acting up.
Draw the vector diagram showing an object on a flat desk moving at a constant speed.
Weight acting down, equal and opposite reaction force acting up, thrust force acting in direction of motion, equal but opposite force of friction acting against the force of motion.
Draw the vecor diagram showing a stationary object on an inclined plane (a slope).
Weight, resolved to act in vertical and horizontal planes (down the slope and at 90 degrees to down the slope), friction acting up the slope (equal but oposite to the component of weight acting down the slope, reaction force acting at 90 degrees to the slope, equal, but opposite magnitue to the component of weight acting at 90 degrees to the slope.
Draw the vector diagram showing an object on an inclined plane moving at a constant speed.
Weight, resolved to act in vertical and horizontal planes (down the slope and at 90 degrees to down the slope), friction acting up the slope (equal but oposite to the component of weight acting down the slope, reaction force acting at 90 degrees to the slope, equal, but opposite magnitue to the component of weight acting at 90 degrees to the slope.
What is a vector quantity?
A quantity with both magnitude and direction
What is a scalar quantity?
A quantity with only a magnitude associated with it
What is the sum of two or more vectors called?
Resultant
Give three examples of scalar quantities
Any three from speed, distance, pressure, temperature, mass, density, power
Give three examples of vector quantities
Acceleration, velocity, displacement, Force, Weight, momentum
State the forces that will act on a helicopter that is moving horizontally
Lift, Air resistance, Weight, Thrust
How can drawn force vectors be arranged to show that an object has constant velocity?
Closed triangle of vectors. This shows the forces are in equilibrium.
What is the difference between a vector quantity and a scalar quantity?
Vector has a direction, scalar does not.
A value with magnitude only is a ________?
Scalar
A value with magnitude and direction is a ____________?
Vector
Distance an speed are examples of _________ quantities
scalar
What is the name given to a vector formed by adding vectors together?
Resultant vector
Force, displacement and velocity are examples of __________ quantities
Vector
What is a contact force?
A force between two object which are touching
What is a non-contact force?
A force between objects which are separated by space.
Give two examples of contact forces
e.g. friction, air resistance, tension, drag, reaction
List three non-contact forces
gravitational, electrostatic, magnetic
The single force which has the same effect as the combination of all the different forces acting on an object is the ______________ _______________.
resultant force
If a body is in equilibrium, what’s the sum of all the forces acting on it?
0
Explain what equlibrium means in the context of a moving object.
Equilibrium means that the moving object will have no resultant force acting on it so it will be moving at a constant speed.
Define weight
The force of gravity acting on an object’s mass
Give the formula which links Weight, mass and gravitational field strength
W = mg
What is the value of g on earth?
9.81 ms-2
What is a moment?
A moment is the turning effect of a force around a turning point
How do you calculate a moment?
moment = F x d
What name is given to a pair of forces of equal size which act perpendicular to each other in opposite directions?
A couple
How can you calculate the centre of mass of an irregularly shaped object?
Hang it from a point, draw a line down, do this 3 times, the point where the three lines meet will be the COM.
How can you use the principle of moments to calculate the mass of a beam?
Hang the beam from a point (not it’s COM) and hang masses from the beam, taking moments around one side will allow you to calulate the moments around the COM.
What is the name of the single point at which an object’s mass appears to act?
centre of mass
The centre of mass of an object is…
the single point at which the objects weight appears to act.
What unit are moments measured in?
N m
What is meant by centre of gravity?
The point in a body where the weight of the object appears to act
Define the moment of a force
Product of the force and the perpendicular distance between the line of action of the force and the turning point
State the principle of moments
The principle of moments states that for a system in equilibrium, the sum of the clockwise moments about a point is equal to the sum of the anticlockwise moments about the same point.
For a uniform regular solid, where will its centre of mass be?
The centre of the object