Speed, Velocity and Acceleration Relationships

March 10th 2010

• What is Speed?

Speed is basically the measurement of an object's motion whether it is accelerating or decelerating and is usually measured in m/s. Speed is found when dividing the covered distance and the amount of time taken to cover it. E.G. The athlete sprinted the 100m race and finished in 10 sec, therefore his speed is:

100 m ÷ 10 sec

= 10m/s

• What is Acceleration and Deceleration?

Acceleration is when an object is starts to speed up. E.g. A skydiver falling would accelerate or generate speed as he/she is falling. Deceleration however, is when an object slows down. E.G. If a skydiver deploys his/her parachute, it will create air resistance causing him/her to slow down or decelerate.

• What is Velocity?

Velocity however, is also the measurement of an object's motion as well as its direction and displacement. Velocity tells us the speed of the object as the direction in which it is going E.G. If a car moves in reverse and covers 70 m in 1 second, the average speed would be 70m/s while the average velocity would be - 70m/s. This is because the car is going in the oppisite direction and therefore has a negative velocity. The speed remains the same since speed is only the measure of how fast or slow an object's motion is and disregards direction.

• What is Terminal Velocity?

Terminal Velocity is basically when an object reaches at a stable and balanced velocity. Take a skydiver for example, he/she will continue accelerating due to the force of gravity that is acting on him/her. The acceleration will come to an end after air resistance starts to increase and balances out the gravitational forces. When that balance had been made then the person would have reached terminal velocity.

• Is there any difference between Speed and Velocity?

Of course there is, but it is not clear or visible. Speed is measuring only how fast or slow an object's motion is, while velocity measures that and the direction of that motion. Look and compare these two graphs:

Graph A:

Graph B:

These two graphs are both a speed graph and a velocity graph respectively. As you can see the difference between these graphs is that one graph measures just the speed of the object and the other measures the speed and direction. One evidence is that in the velocity graph, the velocity goes under zero. This means that the object is going in the opposite direction.

The Speed and Weight on Moon

March 7th 2010

How did I calculate my walking and running speed?

I calculated my walking and running speeds similarly. First, I set up 2 cones at a distance of 10m from each other. Next, I walked the distance while being timed and did the same for running. My running and walking times were then put on the Distance, Speed and Time triangle:

• Walking:

Speed

= Distance÷Time

= 10 m ÷ 5.5 sec

= 1.8 m/s

• Distance:

Speed

= Distance÷Time

= 10 m ÷ 2.47 sec

= 4.1 m/s

Why are our weights different on other planets?

This is because your weight depends on the mass of the planet, the distance you are from the center of the planet and the amount of force that is applied on you while you are on the planet. E.g. On earth, you are applied with 10N of force while on the moon you are only applied with 1.6N of force, therefore your weight decreases while on the moon.

Newton's 3 Laws of Motion

• First Law: The law States that an object in motion will stay in motion as long as there is no unbalanced force acting on it. If a force acts on the object, the object will change speed or direction.

E.G. When a car with luggage that is not properly tied on its top has to suddenly stop, only the car will stop but the rope doesn't provide enough force to stop the luggage from moving therefore causing it to continue moving seeing that there is no unbalanced force acting on it. We humans however are stopped by the seatbelt which provides enough force to stop us from moving.

• Second Law: The law States that if an unbalanced force is acting on an object it will cause it to accelerate in the direction of that force.

E.G. If a person on roller skates is pushed by another person, the person on roller skates will start accelerate in the direction that his partner pushed him to( applied unbalanced force).

• Third Law: Forces always occur in equal or opposite pairs. A moving object will apply force to a stationery object and will cause itself to move corresponding to the amount of force applied.

E.G. If a person is sitting on a wheeled chair(moving object) and pushes his desk(stationery object), he would receive the same amount of force from his desk causing him to move corresponding to the amount of force he had applied.

Mechanical Advantage Worksheet

25th February 2010

Questions:

Answers:

Work and Machines Questions

Tuesday February 16th 2010

Pg 80

Questions:

1. What is meant by:

a)doing work

b)a machine

2. Are you doing work when you are:

a)pushing the mower

b)cleaning your teeth

c)cycling

d)reading this page

Explain your Answers

3. Why must you eat if you are going to keep working?

4. Why are spanners, pliers and can openers called machines?

5.Try to find out the names of other simple machines.

Answers

1.

a)Using a force to move an object

b) anything that makes work easier

2.

a)Yes,because you are applying a force to the mower making it move or change direction.

b)Yes, because you are applying force to the toothbrush thus,moving it and brushing your teeth.

c)Yes, because you're your applying force with your legs to the pedals top move the bike forward and applying force with your arms to the handle bar to steer.

d)No, because your are not applying an force

3.Energy is related to work and is needed when doing work. Food provides energy so work is interdependent upon food and energy to occur.

4.This is because they are a way to make work easier thus being machines.

5.Examples of Simple Machines:

• Incline Plane
• Levers
• Wheel and Axle
• Screw/Nail

Pg 81

Questions

1. What do you need to make a pulley system?

2. Give two reasons why it is easier for a mechanic to lift a car engine out using a pulley system?

3. What is the job of:

a)the chain

b)the gears on a bicycle

4.Turning a bicycle crankshaft turns the back wheel.What is the difference between cycling high gear and low gear?

Answers

1.You need a set of pulley wheels and a rope

2. Two Reasons:

• A pulley is a machine that makes work easier thus making it thus making it easier to lift the engine off the ground.
• Since there is more distance, less force is required to lift the engine off.

3.

a)

• The chain transmits the force applied to the pedals to the back of the wheel, turning them.
• The gears of a bicycle change the number of times that one turn of the crankshaft turns the back wheels.

4. At a high gear, the chain runs over the small cog wheel at the back so that one turn of the crank turns the back wheel several times and is used on flat surfaces. A low gear however is used for climbing steep surfaces and the chain runs on a larger cog wheel therfore turning the back wheel only once or twice.

Pg 82

Questions

1. Which simple machines were used:

a) to split the blocks

b) to move the blocks

c) to put the blocks in place

2.

a)How has friction reduced when the block were moved?

b)A simple invention, first used 700 years after the Pyramid was built, would have reduced friction further. What is it?

3. Draw a diagram to show how to lift a block of stone using a lever.

4.Wedge shaped tools and ramps are still in use. Give some examples of how they are used.

5.How much work had to be done to raise the last block(weighing 25,000 N) on to the top of the pyramid?

Answers:

1.

a)Wedges

b)Huge Ramps

c)Ramps and Rollers

2.

a) By using rollers, the Egyptians were able to reduce the amount of friction. This is because rollers are circular and round and are able to roll on the ground easily, while the blocks were squared and therefore produced a lot of friction when moved on the ground.

b) The Wheel and Axle

3.

4. Wedges are used for lifting and separating E.G. Forks are considered wedges since they split and separate the material ( Food) when used. Other uses for the wedge is for holding fast E.G. A Wedge-type door stopper uses friction to stop a door from moving as well as using it to create a firm grip to the floor.

5. Since the distance is 140m and the amount force needed is 25,000N, therefore:

Work

= Force x Distance

= 25000 x 140

= 3,500,000 Joules

What are Machines ?

Monday February 15th 2010

Forces Questions

Questions:

1. What is a Force?
2. Give 4 Examples of Forces
3. Units of Forces?
4. Equation of a Force?

Answers:

1. A force is basically a push or pull on an object that can either change its direction, speed or shape.
2. Here are a few examples of forces:
   • Friction is an example of a force and happens 2 surfaces are rubbed together causing the object to slow down and producing heat e.g. a car moving on the street creating friction between the tires and the street.
   • Air Resistance is a force that happens between a moving object and air pushing it in a speed and direction dependent on the wind direction and speed e.g. A fast cyclist cycling against the wind.
   • Gravity is a very common example of a force and is an attractive force between objects and the earth and causes an object to be pushed down on the earth depending on its mass; the bigger the object, more the mass of the object and the more the gravity e.g. an apple falling from a tree to the ground.
   • A magnetic field is a force that occurs between a two magnets or a magnet and a magnetic metal (Iron), it causes the magnets to either attract or repel depending on how the magnet's domains are lined up e.g. two magnets beside each other with the same south pole; they will repel.
3. Forces are measured in Newtons
4. Forces Equation:

F=Mass x Acceleration

E.G.

F= 50 KG x 10m/s^2

=9.8 m/s^2