Physics Module 2 Flashcards
What is force?
A push or pull on an object.
What does balanced forces mean?
The forces on an object are at an equilibrium (they cancel each other out). The velocity of the object will not change.
What does unbalanced forces mean?
The object is accelerating or decelerating. (The velocity is changing.)
What does G-force measure?
Acceleration
What is Newton’s first law of motion?
Inertia - an object’s velocity will not change unless acted on by a force. An object wants to keep doing what it’s already doing.
What is Newton’s second law of motion?
F=ma (Force = mass x acceleration). (Net force = force after all other forces have cancelled out.)
What is Newton’s third law of motion?
Every action has an equal and opposite reaction.
What is terminal velocity?
When the force of weight downwards is matched exactly by the force of air resistance upwards. They cancel each other out and the object remains at a constant velocity.
What is inertia?
The resistance to change in velocity.
What is resultant force?
The single force two unbalanced forces are equivalent to. (Force of velocity.)
What is the definition of a Newton?
The force required to give 1kg an acceleration of 1m/s(2).
Do forces only affect motion?
No. They can also affect an object’s shape or volume.
What is static friction?
When the force of friction is greater than the push/pull on the object, and so the object does not move.
What is dynamic friction?
Friction on an object moving across another. This creates heat.
Which type of friction is greater?
Static friction. Once an object starts to move, friction drops.
What is drag?
The friction an object experiences moving through a liquid or gas.
On Earth, how many Newtons does a mass of 1kg weigh?
9.8N (Rounded to 10N)
What is the formula for calculating weight?
W=mg (Weight = mass x gravity)
What are the two meanings of g?
- Gravitational field strength (Newtons per kilogram)
- Acceleration of free fall (metres per second squared)
Since action and reaction forces occur in pairs, why do they not cancel out?
Because the forces in each pair act on different objects, not the same object.
What is momentum?
An object’s tendency to remain in motion
What is the formula for momentum?
p=mv (Momentum = mass x velocity)
What is impulse?
An object’s change in momentum over time (resultant force x time = change in momentum)
Are momentum and impulse scalars or vectors?
Vectors (force is a vector, so they are too)
What formula links force and momentum?
resultant force = change in momentum
time
(resultant force = rate of change of momentum)
This is another way of saying F=ma.
What is the law of conservation of momentum?
When two or more objects act on each other, their total momentum remains constant (provided no external forces are acting).
How do you figure out the velocity of two objects after a collision?
- You figure out each of their velocities before the collision (since they’re moving in opposite directions, one should be positive and the other should be negative - VECTORS!!)
- You add them together, giving you the total velocity before the collision
- Total momentum = total mass x velocity, so velocity = momentum over mass
- Do the division and voila
How do you figure out the resultant force in vector scale drawings?
- You arrange the arrows tip-to-tail in a grid
- You complete the triangle and measure the new side (or use Pythagoras)
- You measure the angle to find the direction (bearing from north), or use SOHCAHTOA
What is centripetal force?
The inward force needed to make an object move in a circle. (NOT produced by circular motion, is required for it)
What is required for centripetal force?
An inwards force that provides the centripetal force. (Examples: String’s tension on a swing-ball. Sun’s gravitational pull on earth. Nucleus’s electrostatic force on electron.)
What is centrifugal force?
The outwards force of an object moving in a circle that does not experience centripetal force (person inside car/washing machine). Is actually just the inertia of an object/lack of centripetal force, not a real force.
What would happen to an object moving in a circular motion is the centripetal force disappeared? (string cut)
It would move along a straight line that is a tangent to the circle
How do we know centrifugal force is not a real force?
We know there is no real outwards force because if there were, if the centripetal force was removed the object would move in a straight line perpendicular to the tangent.
What are the three conditions in which more centripetal force would be needed?
- Mass of object increases
- Speed of object increases
- Circle’s radius decreases
What is the moment of inertia?
An object’s resistance to having the speed of its rotation changed
What decreases the moment of inertia?
Decreasing the average mass around the axis of rotation (pulling arms in = spin faster)
Does a change in velocity mean a change in speed or direction?
It’s a vector, so either.
Why, in circular motion, is an object always accelerating towards the centre of the circle?
Because its direction is always changing, so the velocity is always changing, and so it is always accelerating.
How can an object accelerate towards a point in a circular motion without getting closer to it?
Because it is always moving inwards from the position it would have had if travelling in a straight line.
What is a moment?
The turning effect of a force
What is the formula for the moment of a force?
Moment = F x d
(moment of a force about a point = force x perpendicular distance from the point)
What is a torque?
The moment of a force
What is the principle of moments?
When an object is in equilibrium (balanced), the total clockwise moment about a point equals the total anticlockwise moment about the same point
What are the conditions for equilibrium?
The sum of forces in one direction must equal the sum of forces in the opposite direction. Therefore, the principle of moments must apply.
