2) Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).
What does this mean?
The heavier objects require more force to move the same distance as lighter objects.
3) For every action there is an equal and opposite re-action.
What does this mean?
This means that for every force there is a reaction force that is equal in size, but opposite in direction. That is to say that whenever an object pushes another object it gets pushed back in the opposite direction equally hard.
The rocket's action is to push down on the ground with the force of its powerful engines, and the reaction is that the ground pushes the rocket upwards with an equal force.
Elasticity is the property of solid materials to return to their original shape and size after the forces deforming they have been removed.
"Hooke's Law" is about stretching springs and wires.
When we apply a force to a spring, it stretches.
If we apply double the force, it stretches twice as much, so long as we don't over-do it.
We measure the original length of the spring when we start. When it stretches, we measure the extension - that's how much longer it is than it was when we started.
Extension = present length – original length`
Hooke’s law states:
* The extension of proportional to the force
* The spring will go back to its original length when the force is removed
So long as we don’t exceed the elastic limit
The elastic limit is where the graph departs from a straight line. If we go past it, the spring won't go back to its original length. When we remove the force, we're left with a permanent extension.
Below the elastic limit, we say that the spring is showing "elastic behaviour": the extension is proportional to the force, and it'll go back to its original length when we remove the force.
Beyond the elastic limit, we say that it shows "plastic behaviour". This means that when a force is applied to deform the shape, it stays deformed when the force is removed.
We use Hooke's Law in spring balances, kitchen scales and
Other devices where we measure using a spring.
A force applied to an elastic object, such as a spring, will result in the object stretching and
storing elastic potential energy.
* For an object that is able to recover its original shape, elastic potential energy is stored in
the object when work is done on the object to change its shape.
* The extension of an elastic object is directly proportional to the force applied, provided that
the limit of proportionality is not exceeded :
F = k x e
F is the force in newton (N).
k is the spring constant in newton per metre (N/m).
e is the extension in metre (m).
Mass and weight are different in physics. For example, mass doesn't change when you go to the Moon, but your weight does. Mass shows the quantity, and weight shows the size of gravity.
If you know your mass, you can easily find your weight because
W = mg
where:
* W is weight in Newton (N),
* m is mass in kg, and
* g is the acceleration of gravity in m/s2
Momentum measures the 'motion content' of an object, and is based on the object's mass and velocity. Momentum doubles, for example, when velocity doubles. Similarly, if two objects are moving with the same velocity, one with twice the mass of the other also has twice the momentum.
Force, on the other hand, is the push or pull that is applied to an object to CHANGE its momentum. Newton's second law of motion defines force as the mass times ACCELERATION. Since acceleration is the change in velocity divided by time, you can connect the two concepts with the following relationship:
force = mass x (velocity / time) = (mass x velocity) / time = momentum / time
Multiplying both sides of this equation by time:
force x time = momentum
the difference between force and momentum is time. Knowing the amount of force and the length of time that force is applied to an object will tell you the resulting change in its momentum.
Initially, when any force is applied to a solid, it will resist and remain in its original shape. As the force is increased, the solid will not be able to keep up the resistance and will start to change shape, or become deformed. Just as different types of solids have different elastic properties, they can also withstand different levels of force before being affected. Eventually, if the force is strong enough, the deformed shape will become permanent or the solid will break.
It is the amount of force that is applied to an object, not duration, that will determine if it can return to its initial form. When the solid cannot return to its original shape, it is said to have passed its elastic limit. The elastic limit is the maximum amount of stress that can be endured by a solid that will allow it to return back to normal. This limit depends on the type of material being used. Rubber bands have high elasticity, for example, and thus a high elastic limit compared to a concrete brick, which is almost inelastic and has a very low elastic limit.
1 Rubber bands provide an interesting contrast to springs. On stretching, they do not obey Hooke’s law very precisely. On unloading, they show hysteresis.
2 The experiment must be done with care. Hang a rubber band or length of elastic vertically and attach weights to the lower end. The load must be increased in even steps; as the load is increased, care must be taken to ensure that the rubber is not allowed to slacken. Then the load must be gradually reduced, again ensuring that the rubber does not slacken too much and that it is not stretched more as the load is removed. Unless these precautions are taken, the non-Hooke an behaviour may not show up.
Table 1 shows some typical data. If I plot a graph of extension against load, the points will appear to fall close to a straight line I should be able to see a clear S-shaped curve. The rubber stretches slowly at first, then roughly linearly, then more and more slowly as it becomes stiffer.
Table 1 Stretching a rubber band (original dimensions: 95 mm x 6.0 mm x 0.85 mm)
Load /N
Length /mm
Extension /mm
0
95
0
1.0
112
17
2.0
137
42
3.0
168
73
4.0
207
112
5.0
242
147
6.0
275
182
7.0
306
211
8.0
328
233
Method 1:
Safety -RISK ASSESSMENT
This experiment does not carry many hazards. Bags and coats will be moved out of the way to ensure that no one will trip over them. Whilst loading the elastic band care will be taken to make sure that the elastic band is loading carefully to try and ensure it does not snap. However I will be wearing safety glasses to prevent injuries to my eyes if the band does snap. I will use some kg masses to stop the retort stand sliding of the desk. I will follow all the safety instructions that my teacher gives me.
Do not add more weight than my teacher has told you me.
I will Position the stand so that any falling weights land on the unit and not my foot!
Equipment:
* Elastic clamp stand
* Same rubber bands
* Metal ruler
* Weights
* Mass hanger
* Safety glasses
Independent Variable: Load (kg) the masses which I am applying to the elastic band.
Dependent Variable: Extension (m) to the elastic band
I have used the same equipment throughout the experiment (including the same length elastic band) to ensure that the experiment is as fair as possible. . To ensure that my measurements are as accurate as possible I will use a metal ruler which will be clamped onto the retort stand so that the elastic band will hang next to it
Method
1. I will ensure I have all my equipment in front of me ready to use.
2. I will set up the clamp and stand
3. I will clamp onto the retort stand a metal ruler
4. I will add one elastic band- ensuring the elastic band is new.
5. I will add the mass hanger and measure the 'extension' of the elastic band when it is not loaded.
6. I will allow the elastic band to stretch and stay in position for 60 seconds before taking a reading
7. I will increase the weight by 10g intervals each time. (Subtract the original length by the current extension)
8. I will keep adding weights and taking note of the extension until the rubber band exceeds the elastic limit.
9. Repeat the experiment twice.
Method 2:
Equipment:
* Safety goggles
* Rubber bands
* Metal ring that can be opened and closed
* Bucket
* 20 2p coins
* Ruler
Method
1. I will suspend a rubber band from a cup hook screwed into the top of a doorway.
2. A metal ring that can be opened/closed will now be attached to the suspended band,
3. I will hang a bucket beneath, so that I can add weight.
4. Now I will measure the extension of the rubber band without any weight
5. I will now a 2p coins to the bucket, to see how the weight can affect the extension, I will allow the elastic band to stretch and stay in position for 60 seconds before taking a reading, with my ruler
6. Each time I will add a 2p coin.
7. I will keep adding weights and taking note of the extension until the rubber band exceeds the elastic limit.
8. I'm repeating the test two times, to get an average.
RISK ASSESSMENT
This experiment does not carry many hazards. Bags and coats will be moved out of the way to ensure that no one will trip over them. Whilst loading the elastic band care will be taken to make sure that the elastic band is loading carefully to try and ensure it does not snap. However I will be wearing safety glasses to prevent injuries to my eyes if the band does snap
Variables:
Independent: Mass hung on elastic
Dependant: Length that the elastic extends or retracts.
Controlled: Same conditions – thus the behaviour of the elastic is constant and Temperature of the rubber band
Romanna Karam