Unit 5

Work and Power

Work is the measurement of force * the distance and is measured in Joules, work can only be present if the force and the distance are parallel to each other, . For example if you are climbing up a stair the distance will be the vertical height of the stairs and the force would be your weight. Power is how much work is done in a period of time Power = work/time, and is measured in Watts. For example if a person put in 50J of work in 5 seconds then that is equivalent to 10Watts of power.

Work and Energy Relationship

Work is Equal to the change in Kinetic Energy and is also equal to the change in Potential Energy. So if we know one of them we know the rest, But that does not mean they have the same equation Work is equal to distance * time, and Kinetic Energy is equal to 1/2 mass*velocity^2, and Potential Energy is equal to mass * gravity * height.
Kinetic energy is the energy that has to do with an object moving horizontally, and Potential Energy is the amount of energy an object has at a set height (vertically).
So if an object was on ground level and had a weight of 500N and was going at 5m/s then the object has 2500 Joules.

Conservation of Energy

Energy is neither created nor destroyed. The conservation of energy in similar to the conservation of momentum. You start out and end with the same amount of joules, the only thing different in this case is that the energy changes its form, but is still constant. In a roller-coaster, the first drop is always the highest then the rest do not matter in height as long as they are shorter than the first one. The coaster will keep on going. For example if it started with 1000 Joules of potential energy, when it drops and reaches the ground it still has 1000 Joules but of Kinetic Energy.

Machines

A machine is basically an object which makes it possible for a person to exert little force on an object that needs a big force, but while doing that the distance will also increase making the work similar in both cases  (BigForce*SmallDistance = SmallForce *BigDistance)
Fin * Din = Fout * Dout
Work1 = Work2

If a person where to lift an object straight into a truck and the other uses a ramp, both would be using the same amount of joules, as force the person without a ramp he exerts a big force over a small distance, but with a ramp, the force is smaller with a bigger distance.

Unit 4 blog post

During the month of January we have focused on quiet a few topics, which I personally enjoyed and understood better than previous Units because I found great interest in them.
The topics which we firmly studied where:

• Rotational and Tangential Velocity
• Rotational Inertia 
• Conservation of Angular Momentum 
• Torque 
• Center of mass/gravity 
• Centripetal force

Now let me share my knowledge by explaining everything I have learned in these topics.

Rotational and Tangential Velocity

The difference between Rotational and Tangential velocity is simple, Rotational velocity is the amount of time it takes for an object to make a complete circle. Tangential velocity is just the normal linear speed. 

For example, look at the picture on the left, if the gears where moving, the red gear would have a greater rotational velocity than the blue gear because it will make more turns than the blue gear over a certain period of time. But their tangential velocity will be equal because they are moving at the same amount of notches every second.

Rotational Inertia



Rotational inertia is the amount of force you need to move an object. This is related with the velocity of an object as well. If an object has a great rotational inertia it will have a low velocity vise versa. There are several ways to change the rotational inertia, for example if a person is spinning on a chair, by bringing his arms closer to his body he is decreasing his rotational inertia, and if he is spreading his arm then he increases his inertia because of the mass away from the center of the object.

Conservation of angular Momentum

Conservation of angular momentum is just the same idea of a skater spinning while decreasing her inertia and increasing her velocity, she can change that straight away while keeping the same exact momentum.

Inertia 1 * velocity 1 = Inertia 2 * velocity 2

 Torque

Torque is the force that makes an object rotate on a axis. For example if a ruler is balanced on a axis that means that the net torque adds up to zero, so both sides have the same torque. 

Torque = lever arm * force, so if you want to find out a missing force or lever arm if all the rest are given, you use this formula

lever arm * force = lever arm * force

Center of Mass

Center of mass is the point where the mass is concentrated if the center of mass is over the base of support then therefore, the object will stay stable and not topple over. But if it exceeds the base of support then the object will topple over, the pictures below describes the center of mass toppling over the base of support.

Centripetal force

 A centripetal force is a force that makes an object follow a curved path, the direction of the force is inwards to the center of the curvature of the path. For example in a washing machine, the dryer spins the clothes around in a fast speed then the centripetal force is acting on the clothes but not the water, so the water escapes through the holes in the dryer while, the clothes remain in the dryer by the centripetal force. 

mass of meter stick

During class we where issued an assignment which was to find out the weight of a ruler without using a scale. We started by doing some demo experiment, one was to show an unbalanced torque and explain why.

This picture shows that the right side of the ruler is shorter, so it will have a smaller torque, they both have the same lever arm distance but the right side has a greater torque therefore has the greater toque and rotating the object clockwise.

In the last demo we where asked to add a 100g mass one side and still make it balance, so we just made the balance point closer to the weight so it could balance.

by looking at this picture we can see that the balancing point is closer to the weight. Both torques have to be equal so that the ruler can balance, so if the force of the right side is 100g=1N, and the lever arm is 10cm then the torque is 10Ncm.

We then started our experiment in finding out the weight of the ruler. We set up the exact same experiment at the top. Our point of balance was at the 70 cm point, so the left side had a force of 0.98N and a lever arm of 30cm and the right side had a lever arm of 20 and a unknown force. We found the force by 0.98*30= 29.4, then divided 29.4 by 20 to give us 'x', and that was 1.47. We then divided 1.47 by 9.8 so that we can convert it back to kg and got 0.15kg = 150g.

Center of mass and Rotational Inertia

Center of mass

The Center of mass of an object is the point where all of its mass is concentrated. When an object is supported at its center of mass there is no net torque acting on the body, so it will remain at equilibrium and balance. If the center of mass surpasses the bass it is under, it will lose balance and collapse.

Rotational Inertia

Rotational inertia is a Scalar, this means that it is not a vector and is dependent upon the radius of rotation, it is a measurement of an object's resistance to change in its rotation. Change in rotation before has to equal change in rotation after. So if an object had a great rotational inertia and a low velocity, the same object after can have a low rotational inertia with high velocity so that both change in momentum are equal

Unit 3 Summary

Newton’s 3rd Law and  Action/Reaction Pairs:

Newton's 3rd law states that: "Every action has an equal and opposite reaction". This means that if someone pushes you are pushing back at him with the same force. If you pull something it will pull you back with the same force. If the earth is pulling you, you are pulling the earth with the same force.

Tug of War / Horse and Cart:

If their was a horse pulling the cart along the street the pull on the rope isn't whats making the cart move with the force, as every action has an equal and opposite reaction, so the net force on the rope is 0 (zero). The horse is able to move the cart because the force he is pushing the ground at is greater than the force the cart is pushing the ground at. So the ground will push the horse forward with an equal and opposite force, the same with the cart. So the equal and opposite force of the horse is greater than the equal and opposite force of the cart, so this is house the horse is able to move the cart.

Forces in Perpendicular directions:

If there was a plain flying to the north direction at 10m/s and the air was blowing at 10m/s to the east. The plain would then be going to the North-east direction as it is the exact midway of both forces, and it has both horizontal and vertical forces acting on it. The plain will also be moving at a speed of 14.1, this is because the plain and the wind form and 10, 10, 10 root 2, triangle.

Gravity and Tides:

Tides are manly caused by the moon than the sun this is because, the moon is closer to the earth. This can be explained by this formula G*(m1m2)/(d^2) this formula if applied shows that the sun has a greater force on the earth than the moon does. But the tides do not depend on the amount of force affecting the sides but the difference of the certain point of the earth from the center of the earth.

Newtons 3rd law

This video in my opinion was very useful as the man in the video shows real life situations in which he asks people questions about the gravitational pull between the earth and the moon, and despite these people knowing Newtons 3rd law (every action has an equal and opposite reaction) they still do not apply it to his questions. They think If an object has a greater mass it will has a larger gravitational pull, but i guess they just didn't fully comprehend Newtons law.

tides

Tide Resource.

 Each day the earth experiences 2 high tides and 2 low tides. They come 1 after the other and last for 6 hours each. For example if at 12am there was a high tide, at 6am there will be a low tide and at 12pm there will be another high tide and at 6pm there will be another low tide.

If a place in the earth is experiencing a high or low tide, the completely opposite side of the world will completely experience the same tide, this is due to the difference of the moons gravitational pull on the earths core. 

The tides have to be equal and opposite, or either the tides will not be able to form.

A spring tide is when the sun and moon are acting on the same sides of the earth and cause higher than normal tides, and a neap tide is where the sun and moon are affecting the earth on perpendicular sides and cause normal tides.