Wallace Hall Academy Physics Department Space Pupil Notes Name:
Learning intentions for this unit? Be able to state what the value is for acceleration due to gravity during freefall Be able to explain projectile motion Be able to perform calculations involving horizontally launched projectiles using the equations s = vt and v = u + at Be able to explain orbital motion (in terms of projectiles) Be able to describe the impact and benefits of space exploration Be able to describe how different sections of the Electromagnetic spectrum can be used to give information on astronomical objects and phenomena Be able to identify continuous and line spectra and use them to identify what elements a star is made up of Be able to state the difference between temperature and heat Be able to state what specific heat capacity is Be able to state that different materials require different amounts of heat energy to raise the temperature of the same amount of mass Be able to perform calculations using the equation E h = cm T Be able to state what latent heat is Be able to perform calculations using the equation E h = ml Be able to use conservation of energy to perform calculations about re-entry Be able to state what a light year is and perform calculations using d = vt Be able to describe the evidence there is for the Big Bang Be able to state the age of the universe 2
Acceleration due to gravity When an object falls it experiences two forces. Gravity causes the object to have a weight which pulls it down and as it speeds up it will experience an upward air resistance force. In a group of 2 or 3 discuss what you think will happen if two objects of similar size but different masses are dropped. Which do you think will hit the ground first? Experiment to determine acceleration due to gravity Aim: To determine the value for acceleration due to gravity. Diagram: Method: Results: Exp. 1 Exp. 2 Exp. 3 Exp. 4 Exp. 5 Average acceleration (ms -2 ) Conclusion: Evaluation: 3
PROJECTILE MOTION An object which is fired horizontally from a raised position will accelerate towards the ground at a rate of 9.8 ms -2 due to its weight. There are no unbalanced forces acting horizontally so it travels at a constant horizontal velocity. Draw a diagram below of the path a projectile would follow if fired horizontally from a raised position. The constant vertical acceleration combines with the constant horizontal velocity to produce a curved path. In order to solve projectiles problems we must first split the motion into its horizontal and vertical components. As there is no acceleration horizontally the horizontal motion can be analysed using, s = v = t = In the vertical direction the projectile accelerates due to gravity so a reorganised version of the acceleration equation is used, v = u = a = t = 4
Example 1. A cannonball is fired horizontally from a cliff with a velocity of 20 ms -1. The cliff is 50 m high and the cannonball takes 3 s to hit the water. a. Calculate how far from the base of the cliff the cannonball lands. b. Calculate the final vertical velocity of the cannonball. Graphs of projectile motion The horizontal velocity of a projectile is constant. The vertical velocity of a projectile increases because of acceleration due to gravity. Draw velocity-time graphs of the horizontal and vertical motion of a projectile below. You will remember from the Dynamics topic that the area under a velocity-time graph tells us the displacement of an object. This means the area under the vertical velocity-time graph tells us the height through which an object has fallen. 5
Example 1. A stone is thrown horizontally from a cliff at a horizontal velocity of 4 ms -1 and lands after 3 s. a) Calculate how far away from the base of the cliff the stone will land. b) Calculate the horizontal velocity of the stone after 1.6 s. c) Calculate the final vertical speed of the stone as it lands. d) Draw a velocity-time graph of the horizontal motion (numerical values are required on both axes). e) Draw a velocity-time graph of the vertical motion (numerical values are required on both axes). f) Calculate the height of the cliff. 6
Orbital motion In the 1600 s Isaac Newton conducted a thought experiment that is now dubbed Newton s Cannon. He imagined placing a cannon on top of a mountain and firing a cannonball horizontally. He knew that the cannonball would fall towards the ground at a constant acceleration and also that Earth was a sphere. He reasoned that if the mountain were high enough, and the cannonball fired fast enough, the cannonball would miss the earth and travel right around the planet. This is how orbital motion works. All objects are constantly accelerating towards the centre of their orbit but because of their large velocity they follow circular paths. Satellites The diagram shows a satellite orbiting above the Earth (not to scale obviously). Mark the forces acting on the satellite on the diagram. Satellites use curved reflectors to send and receive signals to and from Earth. There are many types of satellites orbiting the Earth including weather satellites, spy satellites, GPS satellites and communications satellites. There are also geostationary satellites which orbit above the equator and take 24 hours to do so. This means they are always above the same point on the equator as the Earth spins every 24 hours. Low Earth orbit (LEO) satellites orbit up to 2000 km above the Earth. Medium Earth orbit (MEO) satellites orbit between 2000 km and 36000 km above the Earth. Geostationary orbit satellites orbit at 36000 km above the surface of the Earth. 7
Experiment to simulate satellite motion Aim: To determine how orbital height affects orbital time through a model for a LEO satellite at 2 000 km, a MEO satellite at 20 000 km and a geostationary satellite at 36 000 km. Diagram: Method: Results: Conclusion: Evaluation: 8
SPACE EXPLORATION There are 3 ways we currently investigate space, 1. 2. 3. There are many benefits to space exploration but also many risks. In a group of 2 or 3 discuss what you think these benefits and risks are and make a list of them below. Benefits of space exploration Risks of space exploration Explanation of one benefit we get from space exploration Description of 2 inventions we have because of space exploration 9
Spectra By far the safest way of investigating space is to use telescopes to research information about distant objects. All hot objects give off spectra. There are two types of spectra; continuous spectra and line spectra. Continuous spectra Line spectra or Continuous spectra contain all of the visible wavelengths from violet through to red. Line spectra have gaps in the spectra. These gaps are as a result of elements emitting or absorbing very specific wavelengths of light. Each element absorbed different wavelengths so by investigating the line spectra from distant stars we can identify what elements make up the star. We are also able to determine how far away the stars are and how fast they are moving away from us using the spectra. Example The line spectra of some elements are shown below alongside the line spectra from a distant star. State whet elements make up the star. Hydrogen Mercury Neon Helium Star 10
Heat and Temperature One of the major difficulties with manned space exploration is re-entry through the Earth s atmosphere. This because of the high temperatures created because of air resistance. To fully understand this we must first understand the difference between heat and temperature. In a group of 2 or 3 discuss how you would explain what heat and temperature are. Heat is Temperature is. Specific heat capacity Different substances require different amounts of energy to heat them up. This is because of their specific heat capacity. Substances with a lower specific heat capacity are easier to heat up. Substances with a higher specific heat capacity are harder to heat up. The equation which links heat, temperature and specific heat capacity is, E h = c = m = T = 11
Example 1. 3.2 kj of energy are used to raise the temperature of 150 g of copper from its starting temperature of 20 o C. Calculate the final temperature of the copper. 2. 1.34 kj of energy are used to raise the temperature of a sample of aluminium from 16 o C by a further 23 o C. Calculate the mass of the aluminium. 12
Experiment to determine the specific heat capacity of water Aim: To determine the specific heat capacity of water. Diagram: Method: Results: Conclusion: Evaluation: 13
Example 1. A 2.4 kw kettle is turned on for 3 minutes to boil some water from its room temperature starting point of 20 o C. a. Calculate how much electrical energy the kettle turned into heat energy during the 3 minutes. b. Calculate the mass of water which was raised in temperature to its boiling point. c. Explain whether the actual temperature increase of water would have been less than, equal to or greater than the value used in b. 2. Two 3 kw heaters are used to heat up a 2 kg block of aluminium and a 2 kg block of copper for a time of 1 minute. Explain which block would increase in temperature by the largest amount. 14
Latent heat When dealing with changes in temperature it is the specific heat capacity of a substance that is important. When dealing with changes in state it is the specific latent heat that is important. This describes the energy which must be put into or is taken out of a sample to break or make bonds when changing state. E h = m = l = When changing state from solid to liquid or liquid to solid we must use the specific latent heat of fusion. When changing state from liquid to gas or gas to liquid we must use the specific latent heat of vaporisation. Example 1. Calculate how much energy would be needed to melt 3.7 kg of ice into water. 2. Calculate how much energy would be needed to boil 3.7 kg of water into steam. 15
3. A 2.6 kw heater is used to heat a 300 g sample of ice at 0 o C. a. Calculate how much energy is required to melt the ice into water at 0 o C. b. Calculate how much energy is required to raise the temperature of the water from 0 o C to its boiling point. c. Calculate how much energy is required to boil the water into steam at 100 o C. d. Calculate how long this whole process of turning ice into steam would take. e. Explain whether the actual time taken would be smaller than, equal to or greater than the value calculate in d. 16
Experiment to determine how temperature is affected during a change in state Aim: To determine how temperature is affected during a change in state. Diagram: Method: Results: Conclusion: Evaluation: 17
Cooling curves A cooling (or heating) curve shows that there is no change in temperature when a material changes state. Specific heat and latent heat comparison Equation Specific Heat Latent Heat Used when there are changes in. Units 18
Spacecraft Re-Entry One of the major risks with manned space travel is reentering the Earth s atmosphere after the space mission is complete. This is because of air resistance and the fact that there is none in space, meaning the spacecraft is travelling really fast when it reaches the atmosphere. It then encounters massive amounts of air resistance and as a result the kinetic energy of the spacecraft is converted into heat energy. Spacecrafts use special heat shielding to absorb and then re-radiate these large amounts of heat energy so that the spacecraft does not melt upon re-entry. You will notice that the underside and nose of the space shuttle are black as black is better at absorbing then re-radiating heat than white it. Examples 1. A space capsule with a mass of 1440 kg re-enters the Earth s atmosphere at 9,000 ms -1. The capsule has an average specific heat capacity of 2970 J kg -1 C -1. a) Calculate the kinetic energy of the capsule on re-entry. b) If all the kinetic energy is transferred to heat energy of the capsule, calculate the predicted final temperature of the capsule if there is no change of state and the initial temperature was -130 o C. 19
2. A meteor enters the Earth s atmosphere at 30,000 ms -1. It has a mass of 880 kg and is made of a material with a specific heat capacity of 570 J kg -1 C -1. The material melts at 2200 C. a) Calculate the kinetic energy of the meteor. b) Explain what happens to the speed of the meteor as it hits the atmosphere. c) If all the kinetic energy becomes heat energy, and is used to change the temperature of the meteor, calculate the change in temperature of the meteor. d) Explain whether the meteor hits the Earth or not. 3. A spacecraft of mass 875 kg decelerates from 8,000 ms -1 to 2000 ms -1 as it enters the atmosphere. a) Calculate the original kinetic energy of the spacecraft. b) Calculate the final kinetic energy of the spacecraft. c) If the spacecraft travels 1x10 5 km through the atmosphere as it comes into land, calculate the average force due to air friction during this process? 20
The light year Space is obviously very, very large and to help us understand and discuss things on this scale we use a new unit of measurement. A light year is a measurement of distance. A light year is the distance travelled by light in one year. If a star is said to be 6 light years away, it means that the light left the star 6 years ago and is now reaching Earth. You are effectively looking back in time when you look at the stars in the night sky as all of the stars we can see are at least 4 light years away. The vast majority of stars are even further away and the light from the stars that you see will actually have left those stars before you were even born. Calculating how far one light year is in m Examples 1. Our sun is 1.5 x 10 11 m away. Calculate how long it takes light from the sun to reach Earth. 2. The nearest star to us (apart from the sun) is 4.3 ly away. Calculate how far this is in m. 21
Exoplanets An exoplanet is a planet out-with our own solar system. To date over 1000 have been detected. In order to sustain life an exoplanet must exist in the habitable region or Goldilocks region around a star where it is not too hot and not too cold. In a group of 2 or 3 discuss 5 things that would be essential for us to live on another planet. 5 things a planet would need in order for us to live there 1. 2. 3. 4. 5. The Big Bang Scientists believe that the Universe and everything in was created 13.8 Billion years ago by the Big Bang. The Big Bang started in a very small space before an energetic explosion blasted matter and energy outwards. The matter would go on to form together to create the elements and then on to create the stars, planets and moons within our universe. 3 pieces of evidence to support the Big Bang theory 1. 2. 3. 22