P2.3 - Forces In Action Flashcards
How many forces are needed to change shape of an object
2 or more
Plastic material
Does not return to its original shape after the force is removed - become deformed or distorted
Elastic material
Returns to its original shape after the force is removed
Hooke’s Law
Force is directly proportional to extension, within the limit of proportionality
What is limit of proportionality
The point beyond which extension is no longer proportional to force
Elastic limit
A force beyond which the material will not return to its original shape when the force is removed
Spring constant
The ratio of force to extension
Can be said as a measure of the stiffness of a spring
Equation for force exerted by a spring
Force (N) = spring constant (N/m) x extension (m)
F = k x e
Equation for energy transferred in stretching
Elastic potential Energy (J) = 1/2 x spring constant (N/m) x (extension)^2 (m)
E = 1/2ke^2
Gradient on a force and extension graph
Spring constant - the steeper it is the stiffer the spring
area under force extension graph
Elastic potential energy
A f.e graph for an elastic band would be non-linear
True - therefore doesn’t follow Hooke’s Law :)
good work keep going!
Gravitational field
A region where a mass experiences an attractive force
Gravity/weightequation
Gravity/weight (N) = mass (kg) x gravitational field strength (N/kg)
What is gravitational field strength (aka gravity constant)
measure of the force on a 1kg mass when it is is a gravitational field
What is weight?
Force due to gravity which acts upon an object
Gravitational field strength of Earth
10 N/kg
Gravitational field strength on the Moon
1.6 N/kg
Resultant forces on planet equation
Resultant force (N) = Mass (kg) x acceleration due to gravity (m/s^2)
What is gravitational potential energy (G.p.e)
The energy transferred to a gravity store when you lift an object in a gravitational field
G.P.E equation
Gpe (J) = mass (kg) x gravitational field strength (N/kg) x height (m)
Gpe = mgh
G.f.s is always 10 on earth
Moment
The turning effect of a force
Moment equation
Moment (Nm) = force (N) x PERPENDICULAR distance (m)
Moment is a vector
True - it is either CLOCKWISE or ANTI-CLOCKWISE
What is the moment if the force is applied in line with the pivot?
Moment is 0 because it only applies when the force is applied across a PERPENDICULAR distance
Perpendicular distance is indirectly proportional to force applied
Increase P.distance = proportional decrease in force applied
(Vice versa)
Principle of moments
When the anti-clockwise moment is the same as the clockwise moment about the pivot
On a seesaw where would one with lower mass have to sit?
The person with the lower mass would have to sit further away from the pivot and the larger mass would have to sit closer to the pivot
Lever
A force multiplier which transmits forces by rotating about a pivot. It reverses the direction of the input motion so it is opposite in the output
Effort
The force that you exert in a lever (the input motion)
Load
The force that the lever exerts of the load. (The output motion)
If load closer to pivot
Less force needed (and vice versa)
Mechanical advantage
Ratio of load to effort
Mechanical advantage equation
MA (NO UNIT) = load/effort
Gears
Like moment multipliers
Mechanical advantage for GEARS
ma = output cog radius/input cog radius
What is the perpendicular distance in a cog
The diameter
If MA < 1
Speed multiplier
HOW?
- big gear goes to small gear
- lower moment
- output rotation is faster (because small one turns more within one cycle of the large one)
If MA > 1
Torque multiplier
HOW?
- small bear goes to big gear
- higher moment
- output rotation slower (because within many cycles on the small one, the big one only does one)
How did simple machines revolutionise the way things were done?
People were able to complete many tasks easily, using their own effort
Pressure in a fluid equation
Pressure (Pa) = force @ 90 degrees to surface (N) / area of that surface (m^2)
P = F/a
Hydraulic machine
A simple machine which uses a liquid to transmit a force
Composition of a hydraulic machine
2 pistons, a pipe with water- one piston is pushed, pushing the liquid in the pipe and then outputted by the second piston
(Look @ figure 3 on pg 89)
If the output piston is larger than the input one
Output force is larger
If the output piston is smaller than the input piston
Output force is smaller
Example of hydraulic
Car brake
