Do you know your formulae?

Unit 4 Formulae

 

Tell the person next to you…

·         All of the formulae from this unit

o    eg. "The formula that links Wd, F and d is…"

·         All of the quantities from this unit

o    eg. "Wd = Work done"

Answers

·         

All of the units from this unit

o    

eg. "The unit of Work Done is the Joule"

Formulae

·        

Efficiency = Useful E_out/Total E_in x 100

or      Efficiency = Useful E_out/Total E_in

·         Wd = F x d

·         GPE = mgh

·         KE = ½mv²

·         P = E/t       or       P = Wd/t

·         Total E_in = Total E_out

(Principle of Conservation of Energy)

 

 

Quantities and Units

 

·         E_in = Energy input (J)

·         Wd = Work done (J)

·         GPE = Gravitational Potential Energy (J)

·         KE = Kinetic Energy (J)

·         F = force (N)

·         d = distance moved in the direction of the force (m)

·         m = mass (kg)

·         g = gravitational field strength (N/kg)

·         g_earth = 10N/kg

·         h = height (m)

·         v = velocity (m/s)

·         P = power (W)

·         t = time (s)

Advantages and Disadvantages of Energy Resources.

Begin forwarded message:

ADs and DISADs of ENERGY SOURCES-answers.docx Download this file

4.16

·         

4.16 understand the energy transfers involved in generating electricity using:

·         wind

·         water

·         geothermal resources

·         solar heating systems

·         solar cells

·         fossil fuels

·         nuclear power

wind energy story.swf Download this file

Teacher Presentation.ppt Download this file

Entrance Activity

Starter.ppt Download this file

Starter for 4.16

DragnDropEnergy.swf Download this file

4.15

P = Wd / t

P = E / t

P = Power (Watts)

Wd = Work Done (Joules)

E = Energy Transferred (Joules)

t = Time (s)

4.14

 describe power as the rate of transfer of energy or the rate of doing work

"Rate" just means "divided by time" (see Entrance Activity)

So

Power = Energy / Time

or

Power = Work done / Time

Entrance Activity Answers

Tell the person next to you...

·         You can run up the stairs in the Science block in 30 seconds.

·         Mr. Roff can run up the stairs in the Science block in 20 seconds.

·         Who is the most powerful?  Why?

·         Mr Roff.  He does more work running up the stairs (because has a higher weight) in a shorted time so he is more powerful

 

·         It takes 2 minutes to fill the 20 litre sinks in this room with water. 

·         How fast is the sink filling?

·         10 litres/min

·         At what rate is the sink filling?

·         10 litres/min

·         How long would it take to fill a 10 litre sink?

·         1 min

Power questions

PFY, p. 120

 Power is the rate of doing work. Power (in watts) = work done(in joules)/ time (in seconds)

 1 watt is a rate of working of one joule per second.

 13) p= e/t   5=p/1000= 5000 W  p= 1000/5 p= 200

 14) p= e/t p= 600/6 p= 100w

 15) p = e/t p= 30000/4 p=7500 w

CoE questions

PFY p.121

 19a) 50 x 10= 500N

                b) GPE= mgh  gpe= 10 x 50 x 4  gpe= 2000 J
                c) KE=0.5 x m x v2  0.5 x 50 x v2 25 x V2

Collins, p.91

                 Q3a) GPE= mgh GPE= 35 x 10 x 30 GPE= 10500 J

            b) KE= 0.5 x 35 x v2  10500= 0.5 x 35 x v2

                v2 = 600 v = 24.5 m/s

            c) Some of the energy is lost through friction

4.13

understand how conservation of energy produces a link between gravitational potential energy, kinetic energy and work

CoE.ppt Download this file

4.12

KE formula.ppt Download this file

4.12 recall and use the relationship:

kinetic energy = ½ × mass × speed2

KE = ½ × m × v2

4.11

recall and use the relationship:
gravitational potential energy = mass × g × height
GPE = m × g × h

GPE formula.ppt Download this file

4B2 highest to lowest GPE.swf Download this file

4B2 GPE calculation of car moving downhill.swf Download this file

4.10

·         

4.10 understand that work done is equal to energy transferred

PFY p.112

                                    2) Wd=F x d 

                               5 x 2 = 10J

Wd= F x d 

500 x 40 = 20,000 J

energy transfers = GPE --> kinetic

 1)  Wd = F x d 

                                          50,000= 400 x d

                                d= 50,000/400 = 12500 m

4.9 recall and use the relationship between work, force and distance moved in the direction of the force

work done = force × distance moved         

·  

Wd = F × d

Work formula.ppt Download this file

4B1 work done skiing downhill.swf Download this file

4B1 work done pushing a wheelbarrow.swf Download this file

Starter Qs answers

Tell the person next to you...

·         Imagine pushing a king sized bed from one side of the classroom to the other

·         Would it make you feel tired? 

o    Yup!

·         Would you have to work hard to push it?

o    Yup!

·         What could you change so you have to do less work pushing?

o    Anything that decreases the force needed (reduce friction by putting wheels on it, ice under it, etc)

o    Anything that decreases the distance travelled (only push it half way!, etc)

o    So the formula for work must contain force and distance

Plenary Questions

4.8

·         

describe how insulation is used to reduce energy transfers from buildings and the human body

Task 1

·         Use this interactive animations to investigate how different insulation affects the rate of cooling of hot water

<<Cooling of hot water with insulation - interactive.swf>>

Task 2

·         Use these interactive animations to find out about the energy transfers in a house

	<<Types of energy transfers in a house - interactive.swf>>		<<Insulation in a house - % heat losses and savings.swf>>

Task 3

·         Test your knowledge with this quiz

<<Quiz - Types of energy transfers in a house.swf>>

Types of energy transfers in a house - interactive.swf Download this file

Quiz - Types of energy transfers in a house.swf Download this file

Insulation in a house - % heat losses and savings.swf Download this file

Cooling of hot water with insulation - interactive.swf Download this file

4.7

 4.7 describe the role of convection in everyday phenomena

Lee cycles towards the sea ... and back worksheet.pdf Download this file

·   

Convection in a room with a radiator.swf Download this file