Introduction to Mechanics

Question 1

What is a scalar quantity

Answer 1

A quantity that only has a magnitude, without direction

Question 2

What is a vector quantity

Answer 2

A quantity that has both direction and magnitude

Question 3

Give some examples of Scalar Quantities

Answer 3

• Distance
• Speed
• Mass
• Temperature

Question 4

Give some examples of Vector Quantities

Answer 4

• Displacement
• Velocity
• Force/weight
• Acceleration

Question 5

What is a resultant vector

Answer 5

Two forces added together

Question 6

What are the two methods for finding the resultant of two forces

Answer 6

• Scale drawings
• Pythagoras + Trigonometry

Question 7

How can the resultant of two forces be found using scale diagrams

Answer 7

• Draw the two forces end to end
• Draw the resultant force
• Measure the length of the resultant force and the angle from the horizontal

Question 8

What is Resolving a force

Answer 8

Splitting a force into horizontal and vertical components

Question 9

State the two conditions necessary for an object to be in equilibrium and for each condition explain what happens if it is not met

Answer 9

• 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

Question 10

Describe the motion of an object if it is in equilibrium

Answer 10

The object has no resultant force and therefore it is either at rest or moving at a constant velocity

Question 11

How can the forces acting on a object be shown to be in equilibrium

Answer 11

• 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.

Question 12

What is the difference between mass and weight

Answer 12

• 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)

Question 13

Describe how to calculate the parallel component and perpendicular component of an object on an incline plane

Answer 13

Question 14

What is a moment

Answer 14

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

Question 15

Equation of a Turning Moment

Answer 15

M = f x d

Moment (Nm) = Force(N) X Perpendicular distance to line of action of force from the point (m)

Question 16

What is a couple

Answer 16

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

Question 17

What is a pivot

Answer 17

The point about which an object rotates

Question 18

What does the principle of moments state

Answer 18

For an object in equilibrium, the sum of anticlockwise moments about a pivot is equal to the sum of clockwise moments

Question 19

What is the centre of mass of an object

Answer 19

The point at which an object’s weight act, or the point of a point around which the pull due to gravity is zero

Question 20

Where is the centre of mass of a uniform object

Answer 20

It’s centre of mass will be exactly at its centre

Question 21

Is the centre of mass always on an object

Answer 21

No, sometimes it is out an object

Question 22

How can the centre of mass of a regular object be found

Answer 22

Look at the lines of symmetry, the centre of mass is where the lines cross