Topic 9 - Forces and their Effects
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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