Topic 9 Forces Flashcards
What are contact and non contact forces
Contact
A force which acts between objects that are physically touching
Non contact
A push or a pull that acts on an object due to the interaction with another object
What are examples of contact forces and their definitions
Contact
Friction - Is a force that opposes motion
Air resistance - Friction in the air
Tension - Is a force that pulls two objects connected by a length, such as a string or rope
Reaction force / Normal force - Is a force that pushes touching objects apart
What are examples of non contact forces and their definitions
Non contact
Gravitational force - The attractive force experienced by two objects with mass
Electrostatic force - A force experienced by charged objects which can be attractive or repulsive
Magnetic force - A force experienced between magnetic poles that can be attractive or repulsive
In a free body force diagram where does the arrow start from and what does the length of the arrow suggest
centre of mass
The amount of that force - longer arrows mean more force
Describe situations where forces can cause rotation
Forces acting on objects balancing on a fixed point - such as the hinge of a door or a see-saw - may make that object rotate. We call this “turning effect” of a force the moment.
Recall and use the equation:
Moment of a force =
moment of a force (newton metre, N m) = force (newton, N) ×
distance perpendicular to the direction of the force (metre, m)
Recall and use the principle of moments in situations where
rotational forces are in equilibrium:
the sum of clockwise moments = the sum of anti-clockwise
moments
for rotational forces in equilibrium
How do gears work, including ones with long and short radiuses. Also include what happens to the moment and what happens when 2 gears are connected and one turns clockwise
Longer radius = larger gear = more teeth
Longer radius = lower speed of rotation
Smaller radius = high speed of rotation
If 1st one turns clockwise, the 2nd one turns anticlockwise
M = fd, so distance is the radius. Longer radius = larger moment
How do levers transmit the rotational effects of forces
A simple lever could be a solid beam laid across a pivot. As effort is applied to rotate one end about the pivot, the opposite end is also rotated about the pivot in the same direction. This has the effect of rotating or lifting the load.
Levers such as this one make use of moments to act as a force multiplier. They allow a larger force to act upon the load than is supplied by the effort, so it is easier to move large or heavy objects.
