# SP9 - Forces and their Effects ✓ Flashcards

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

Contact forces

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

Normal contact force

SP9a - What are the three non-contact forces?

- Gravitational fields
- Static electricity
- Magnetism

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

A force field.

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

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

- 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.

SP9c - What is the formula for a moment?

Moment (N m)

=

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

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

It is in equilibrium

SP9c - What is the principle of moments?

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

[When a system is in equilibrium]

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

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

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

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

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

- 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.

SP9c - Why is a longer lever more effective?

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

- Increase the turning force
- Decrease the force required to produce the same turning force