P2.3 Flashcards
What is a deformation if it is elastic or plastic?
Elastic deformation: object returns to original shape after force exerted on it
Plastic deformation : object permanently distorted after force has been applied to it and does not become original shape.
What Is stretching, compressing or bending an object? What does it require?
This is when you use more then two forces acting at the same time, like in a spring. They are DEFORMATIONS
Hooke’s law
Limit of proportionality vs elastic limit
The extension of an object deforming elastically is DIRECTLY
Proportional to the force on the object, until you reach the limit of proportionality- where after this the force is no longer proportinal to the extension .
You will see after this point, it will continue to still slightly deform elastically, until a point after this , called the elastic limit, which after this point more force added will distort it (meaning it won’t return back to its original shape). (X).
The elastic limit is the maximum force that can be exerted without it being deformed plastic.
Equation for force exerted by a spring, and what this means anyways.
1) why is force directly proportional to spring (weight hanging analogy) ?
Also what is spring constant
1) when a mass hanging by spring, it exerts its weight downwards, and the spring also then exerts an equal force On the mass. Now if you double this force, the extension will double too, showing that force is directly proportional to extension here…
The force exerted by a spring (N)= spring constant (N/M) x extension (M)
The greater the spring constant, the more a spring can stretch before becoming plastic deformed.
What would graph of force against extension look like.
What does higher or lower gradient mean in terms of spring constant ?
Briefly go through PRACTICAL to investigate Hooke law
1) This would be a linear line through the origin , y=x, where the gradient shows the spring constant, but only until a certain point (limit of proportional), then not for a bit more then (the elastic limit) and here more will mean it becomes plastic
2) steeper the gradient, the higher the spring constant
3) with spring attached to clamp stand, add masses, record original spring length, and extension is new- initial. Then plot graph, use goggles in case spring brakes and mass fall down . Attach ruler as well
Work is done when an object gets deformed (elastic/plastic)
What is equation for energy transferred by spring ?
How can you calculate this using a graph?
Energy (J)= 0.5 x spring constant (N/m) x extension2 (m2)
(It could be compression instead of extension btw)
2) area under force / extension graph = energy transferred in stretching (for the elastic bit)
Other materials graphs : rubber (like elastic band)
Copper and glass
Designs. For tennis racquet vs crash barrier?
Rubber is not proportional to force and does not obey Hooke law. It is curved like x3 quadratic graph. Think of it like a bloom, you blow it up (apply pressure), but it diesn’t really extend that much, but then suddenly it does by a lot in the middle, but finally at the end it becomes hard to extend again… this is why
2) glass just a straight line but it’s spring constant is very very high, then breaks
3) copper similar to spring in terms of how graph looks, but it is a hook.
4) as all materials store energy when they deform, scientists can manipulate what happens next. Tennis raciest let it back, whereas crash barriers don’t return to original shape and return it so it can absorb the impact. Permanently deformed straight away…
Scientists design materials in terms of how they want them to react, so like a tennis racket will return to its shape to do work, but like a bumper of a car will want to permanently deform to absorb impact, so yeh
What is a gravitational field?
This is principle of gravity. It is a region where a mass experiences an attractive force- and ALL MATTER HAS ITS OWN GRAVATAIONAL FIELD WHICH ATTRACTS. But more mass, bigger field.
Equation for force exerted by gravity (basically weight ) and for acceleration due to gravity too
Also what factors increase this gravity force?
Weight )
Gravity force (N)= mass (Kg) x gravational force (N/Kg)
Earth= 9.81 /10
Force becomes bigger if
: mass bigger
: gravitational field strength bigger
: distance between two objects decrease (common sense)
What is and what is the equation for gravitational potential energy?
When an ibject is lifted, energy is transferred to their gravity (Potential energy )store
Potential energy (J) = height (m) x mass (kg) x gravitational field strength (n/kg)
Moment (turning force ) equation
Principles of moments
Moment (NM) = fierce (n) x distance (M) (SIT IS A VECTOR !!!,)
Moment of a force is the TURNING EFFECT is has around a pivot
The distance used must be perpendicular to the line of action of the force, or else it won’t work. Just extend a line in the direction the force is going, then draw a line to connect it to pivot. This is the distance you use
Princiniple of moments= anti-clockwise moment = to clockwise moment, and object is balanced like seesaw
A lever allows for a turning force to be transmitted across a pivot, making it a force MULTIPLIER
How does it work
Moment 1= moment 2, so if you put in a few N of force over a large distance, then the other pivot make it less distance, the force will be multiplied and makes it easier to pick something up
This is weird but for levers…
What is load , effort and therefore mechanical advantage
What can you use to double check your work?
Basically mechanical advantage is just the advantage you get by using a lever= how many times your force was multiplied. To do this, do output force/ input force which is also load/ effort
This could be ratio of distances to double check your work
If levers are force multipliers, what are gears?
Also what are torque multipliers, speed multipliers, and how is mechanical advantage calculated
Gears are Moment multipliers. This is how they work:
1) a force out into one cog, due to newton law this force will be exerted by the other cog too.
2) the two dogs will have different radius or teeth, based on this, the moment will get multiplied but the force stays the same.
Three gears keep the same direction of it.
1) mechanical advantage this time will be the output moment over the input moment, and if this is more then 1, it is a torque multiplier, but if it is less then 1, it is a speed multiplier. SINCE FORCE IS ALWAYS SAME IN GEARS, mechanical advantage is just ratio between the two
Advantage of using speed or torque multiplier think of a bike, speed for uphill, downhill torque…
Pulleys
Force multipliers too
