Introduction to Mechanics Flashcards
What is a scalar quantity
A quantity that only has a magnitude, without direction
What is a vector quantity
A quantity that has both direction and magnitude
Give some examples of Scalar Quantities
- Distance
- Speed
- Mass
- Temperature
Give some examples of Vector Quantities
- Displacement
- Velocity
- Force/weight
- Acceleration
What is a resultant vector
Two forces added together
What are the two methods for finding the resultant of two forces
- Scale drawings
- Pythagoras + Trigonometry
How can the resultant of two forces be found using scale diagrams
- Draw the two forces end to end
- Draw the resultant force
- Measure the length of the resultant force and the angle from the horizontal
What is Resolving a force
Splitting a force into horizontal and vertical components
State the two conditions necessary for an object to be in equilibrium and for each condition explain what happens if it is not met
- Result force must be zero otherwise the object will accelerate/change direction
- The sum of anticlockwise moments must be equal to the sum of clockwise moments otherwise the object will rotate
Describe the motion of an object if it is in equilibrium
The object has no resultant force and therefore it is either at rest 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
- 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 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.
- Weight(N) = Mass(kg) x Gravitational Field Strength (N/kg)
Describe how to calculate the parallel component and perpendicular component of an object on an incline plane
What is a moment
The turning effect of a force around a point, which is the force multiplied by the perpendicular distance from the line of action of the pivot
Equation of a Turning Moment
M = f x d
Moment (Nm) = Force(N) X Perpendicular distance to line of action of force from the point (m)
What is a couple
A pair of coplanar forces (meaning they are forces within the same plane), where the two forces are equal in magnitude but act in opposite directions
What is a pivot
The point about which an object rotates
What does the principle of moments state
For an object in equilibrium, the sum of anticlockwise moments about a pivot is equal to the sum of clockwise moments
What is the centre of mass of an object
The point at which an object’s weight act, or the point of a point around which the pull due to gravity is zero
Where is the centre of mass of a uniform object
It’s centre of mass will be exactly at its centre
Is the centre of mass always on an object
No, sometimes it is out an object
How can the centre of mass of a regular object be found
Look at the lines of symmetry, the centre of mass is where the lines cross
