P8: Forces in Balance

Question 1

What is a scalar quantity?

Answer 1

A quantity with magnitude only

Question 2

What is a vector quantity?

Answer 2

A quantity with magnitude and direction

Question 3

What is a force?

Answer 3

A push or a pull that acts on an object due to the interaction with another object.
They are vectors.
Influence that can change the motion of an object.

Question 4

What is a contact force?

Answer 4

A force which must be touching another object to act
e.g. friction, air resistance, tension

Question 5

What is a non-contact force?

Answer 5

A force that does not require two objects to be touching to act.
e.g. gravity, magnetism, electrostatic

Question 6

What is a normal contact force?

Answer 6

Only happens if two objects are in direct contact, if an object exerts a force on another, the other object will exert the same force in the opposite direction, called the normal contact force

Question 7

What is a resultant force?

Answer 7

A single force that has the same effect as all of the original forces acting together

Question 8

What is Newton’s First Law?

Answer 8

If the resultant forces on an object are balanced, then the object is at rest, if stationary, or moving at constant velocity, if in motion

Question 9

What is a free body diagram?

Answer 9

A diagram, where the object is modelled as a point and the forces acting on it are modelled as arrows in the direction that the force is acting in. Their size is proportional to the size of the force.

Question 10

How do you find the vertical and horizontal components of a force?

Answer 10

vertical (y)/ perpendicular component = sin(x)force
horizontal (x)/ parallel component = cos(x)force

Question 11

What is a moment?

Answer 11

The turning effect of a force

Question 12

What is the formula for a moment?

Answer 12

Moment = Force * Distance from pivot
(Nm) (N) (m)

Question 13

What needs to be kept in mind when calculating the moment?

Answer 13

The distance needs to be perpendicular to the line of action of the force on the pivot

Question 14

Why do certain objects topple?

Answer 14

The weight of an object is directly down from its centre of mass - if the block is turned, there comes a point where the line of action of the weight lies just outside the base of the object, causing an unbalanced moment.
It’ll topple if its centre of gravity is outside its base. bad
(If the position of the centre of mass changes, the line of action of the weight also changes. If line of action of the weight changes, it will produce a resultant moment.)

Question 15

What are levers?

Answer 15

Force multipliers - they allow a heavy object to be moved/lifted by applying a small force. They do this by increasing the distance from the pivot, thus increasing the moment

Question 16

What is the purpose of gears?

Answer 16

To transmit the turning force between objects.

Question 17

What does the turning effect of a gear depend on?

Answer 17

The distance between the edge of a gear and its centre.
If the radius is larger, the turning effect is greater.
The smaller the gear, the faster it spins
(the work done by the two gears should be the same)

Question 18

What is true about the moment of an object if it’s balanced/ in equilibrium?

Answer 18

The total clockwise moment about a pivot = total anticlockwise moment.