Topic 9 - Forces and their Effects

Question 1

SP9a - What do you call forces between objects that are touching?

Answer 1

Contact forces

Question 2

SP9a - What is the name for the regular upward force form the ground when you’re standing?

Answer 2

Normal contact force

Question 3

SP9a - What are the three non-contact forces?

Answer 3

• Gravitational fields
• Static electricity
• Magnetism

Question 4

SP9a - What do all objects that produce a non-contact forces have?

Answer 4

A force field.

An area around an object in which another object could experience a force.

Question 5

SP9a - Describe how the gravitational pull between the earth and the moon are action-reaction forces.

Answer 5

• Force is a vector quantity.
• The force of the moon on the earth is the same size as the earth on the moon but they are in opposite directions.
• Neither objects move in the direction of the force.

Question 6

SP9c - What is the formula for a moment?

Answer 6

Moment (N m)

=

Force (N) x distance perpendicular to the pivot (m)

Question 7

SP9c - What could you say when weights around a pivot are balanced?

Answer 7

It is in equilibrium

Question 8

SP9c - What is the principle of moments?

Answer 8

The some of clockwise moments = the sum of anti-clockwise moments

[When a system is in equilibrium]

Question 9

SP9b - How do you work out the direction and size of the resultant force using the component forces?

Answer 9

The Parallelogram method:

• (If the start of a diagram hasn’t already been provided, draw to the two forces using a scale)
• Draw another pair of dashed-lines parallel to the forces
• This should form a parallelogram
• Draw a line from the object to the vertically opposite corner
• Measure this line and use the scale to work out the size
• If required, measure the angle to show the direction

Question 10

SP9b - How do you resolve the component forces using the resultant force?

Answer 10

The Rectangle method:

• Draw faint horizontal and vertical lines fom the object
• Measure the angle from the horizontal/vertical that the object is at
• Using a scale, draw a line the represent this force
• Draw lines down and across from where this line ends to the horizontal and vertical respectively
• Measure out the length from the object to each of these poitns
• Use the scale to work out the size

Question 11

SP9c - Explain why using two different sized gears in a car may be beneficial.

Answer 11

• The first smaller gear can be connected to the motor
• The second larger gear recieves the moment (turning force) from the first gear
• Since the second gear is larger, it will have a larger radius.
• This means that its moment will be greater (M = F x d)
• Therefore it will transfer more turning force to the wheels of the car.

Question 12

SP9c - Why is a longer lever more effective?

Answer 12

• The formula for a moment (the turning force) is M = F x d
• Thus, by increasing the distance form the pivot, you will either:

1. Increase the turning force
2. Decrease the force required to produce the same turning force