Forces Flashcards
Newton’s first law
An object has a constant velocity or is stationary unless acted on by a resultant force
Changing direction = resultant force
Newton’s second law (force formula)
Force = mass x acceleration
The resultant force acting on an object is proportional to the mass of the object
Force and acceleration is in the same direction
This links to Newton’s first law, because if force = 0 then acceleration must be zero too
Newton’s third law
Every action force has an equal and opposite reaction force
For example, a body falling
- No air resistance only acting on its weight
- Acceleration increases therefore there is now air resistance
- Air resistance increases therefore the air resistance and weight is balanced (equal) this is called terminal velocity
- Parachute opens air resistance is significantly higher than the weight (slows down) this causes upwards acceleration
- Forces balance out again reaching a much slower terminal velocity
Deformation
When a force changes the speed, shape and direction of motion of an object
Force - a force is a push or pull that causes a change in speed, direction or shape of an object
Resultant forces
When the force is going in the same direction they should be added together
When the forces are going opposite direction meaning they should be subtract
Remember if both forces are the same it remains stationary
Driving force (forward force) = 45N
Air resistance (backward force) = 12N
45N-12N=33N therefore its moving 33N forward
Friction
It’s a force between two surfaces which delays/impedes motion which causes heating (air resistance is a type of friction)
It also acts on an object moving through gas and liquid
Hookes law experiment
Measure the original length of a spring
Add known weight to that spring
Measure the new length of the spring
Repeat the experiment using different weights
And plot the average extension
Hookes law theory
Hookes law when the extension of the spring is proportional to the force applied
F=kx when k is constant
F being force/weight (N)
X being the extension (m)
K being the gradient, spring constant (Nm^-1)
Elastic deformation is when the line should be linear, straight line (as it obeys Hookes law)
However there is a point when it stops being linear which is called limit of proportionality, thefore not following Hookes law
Plastic deformation is an example of when Hookes law is not followed
What is a moment (turning effect)
A moment is the turning effect of a force this occurs when object move around a pivot
What is the formula and unit, and what does the moment depend on
Moment of force (Nm) = force (N) x perpendicular distance from the pivot (m)
Remember
- a vertical force will not cause the object to move (when the force is directly facing/away from the pivot)
- since we are multiplying the force and perpendicular distance when the perpendicular force is the furthest away the more moment it has
Therefore more like to turn that way This also applies to force (the bigger the force the more likely its gonna turn that way)
Example of moment using a balancing beam
on the left of the balancing beam the weight is 2N and its 2 metres away from the pivot (remember pivot is symbolised by a triangle)
on the right of the balancing beam the weight is 3N and its 1 metre away from the pivot
Remember the formula is: Mf = F x pd
Therefore on the left of the balancing beam is 2 x 2 = 4
on the right of the balancing beam is 3 x 1 = 3
Meaning the balancing beam will turn towards the left side, which is anticlockwise
the principle of moment
Principle of moment: when the sum of the anti-clockwise and the clockwise pivot equals the same it will stay stationary
What does it mean when an object is in equilibrium and what are the conditions for it
When an object is in equilibrium it means that the object will keep doing what it is doing
- if its stationary it will stay stationary
- if its moving it will stay moving in a straight line
The conditions is that
- their must be no resultant force/the forces on an object must be balanced (forward force = backward force)
- Principle of moment: when the sum of the anti-clockwise and the clockwise pivot equals the same it will stay stationary
What is the centre of mass and how do u find it
The centre of mass is when the point through which the weight of that object acts
Regular shapes find the lines of symmetry and the intersection is the centre of mass
Irregular shapes: hang an the irregular object from the location it has been hanged drop a plumb line and mark it on the object
Then hang at different places (not to close together) and repeat the intersect of those lines is the centre of mass
Stability, types of equilibriums
Toppling - the position of the centre of mass affects whether or not it topples over easily, once the centre of mass gravitational line is outside the body it topples over
To increase stability you can..
- lower the centre of mass
- increase the area of its base
Stable equilibrium
- if when slightly displaced and then released it will turn back to its original place
Neutral equilibrium
- when the object does not move at all when displaced a bit and released this is because there is no moment
Unstable equilibrium
- - if when slightly displaced and then released it will move further away from the original place
