The Arctic is Melting
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- Flora Davis
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1 The Arctic is Melting 1 Arctic sea has shown a large drop in area over the last thirty years. Japanese and US satellite data Jerry Gilfoyle The Arctic and the Length of Day 1 / 42
2 The Arctic is Melting 1 Arctic sea has shown a large drop in area over the last thirty years. 2 In fall, 2013 the first large sea freighter MS Nordic Orion was able to use the Northwest Passage. Japanese and US satellite data Jerry Gilfoyle The Arctic and the Length of Day 1 / 42
3 The Arctic is Melting 1 Arctic sea has shown a large drop in area over the last thirty years. 2 In fall, 2013 the first large sea freighter MS Nordic Orion was able to use the Northwest Passage. 3 Scattered news reports of transfer of Pacific species to the Atlantic. Japanese and US satellite data Jerry Gilfoyle The Arctic and the Length of Day 1 / 42
4 The Arctic is Melting 1 Arctic sea has shown a large drop in area over the last thirty years. 2 In fall, 2013 the first large sea freighter MS Nordic Orion was able to use the Northwest Passage. 3 Scattered news reports of transfer of Pacific species to the Atlantic. 4 Greenland is also melting. Japanese and US satellite data GRACE data Jerry Gilfoyle The Arctic and the Length of Day 1 / 42
5 The Arctic is Melting 1 Arctic sea has shown a large drop in area over the last thirty years. 2 In fall, 2013 the first large sea freighter MS Nordic Orion was able to use the Northwest Passage. 3 Scattered news reports of transfer of Pacific species to the Atlantic. 4 Greenland is also melting. 5 The ice in and around Antarctica is shrinking too. GRACE data Japanese and US satellite data GRACE data Jerry Gilfoyle The Arctic and the Length of Day 1 / 42
6 How Do You Measure Climate Change? Much of the Earth s weather is driven by the Earth s rotation and reflects the interplay of air, water, and ice. This interplay might be used as a tool to measure the impact of climate change. Suppose you are developing a proposal for the National Science Foundation to study the impact of climate change by measuring the change in the Earth s rotation, i.e. the length of day (LOD). Your high-precision clock can detect changes in the LOD as small as ms (1 ms = 10 3 s). The measured rate of loss of Arctic sea ice is shown in the plot. Will your instrument be able to measure any change in the average size of the Arctic sea ice in one year of operation? National Snow and Ice Data Center Jerry Gilfoyle The Arctic and the Length of Day 2 / 42
7 Melting Ice - Rotating Earth Consider a model of the Earth consisting of a uniform sphere covered by water with a thin, circular ice cap at the North Pole floating on the water and symmetric about the rotation axis. If the ice melts, the water is evenly distributed over the all-ocean Earth. The initial ice cap mass is m 1 = kg, its surface mass density is σ = kg/m 2, and its angular size is θ 1 = 13.0 (see figure). The density of water is ρ water = 10 3 kg/m 3. The moment of inertia of the ice cap is I c = (8/3)πσR 4 E (2 + cos θ 1) sin 4 (θ 1 /2). 1 The ice cap shrinks by 0.1 and loses m = kg. How much does the radius change? 2 How much does I E of the Earth change? 3 How much does I c of the ice cap change? 4 What happens to the LOD after the melting? 5 Should NSF fund you? Jerry Gilfoyle The Arctic and the Length of Day 3 / 42 θ
8 Rotational Quantities Jerry Gilfoyle The Arctic and the Length of Day 4 / 42
9 Linear Rotational Quantities Linear Rotational Quantity Connection Quantity s s = rθ θ = s r v T v T = rω ω = v T r = dθ dt a a T = rα α = a T r = dω dt F = m a τ = rf τ = I α KE = 1 2 mv 2 KE R = 1 2 I ω2 p = m v L = r p L = I ω Jerry Gilfoyle The Arctic and the Length of Day 5 / 42
10 How Fast Will the Star Spin? The pulsar in the Crab nebula has a period T 0 = s and this period has been observed to be increasing by T = s each year. Assuming constant angular acceleration what is the expression for the angular displacement of the pulsar? What are the values of the parameters in that expression? What is the torque exerted on the pulsar? The moment of inertia of a uniform sphere is I s = 2mr 2 /5. m C = kg r C = m Jerry Gilfoyle The Arctic and the Length of Day 6 / 42
11 A Pulsar Jerry Gilfoyle The Arctic and the Length of Day 7 / 42
12 F a F = m a Force and Motion 2 Good data Jerry Gilfoyle The Arctic and the Length of Day 8 / 42
13 Linear Rotational Quantities Linear Rotational Quantity Connection Quantity s s = rθ θ = s r v T v T = rω ω = v T r = dθ dt a a T = rα α = a T r = dω dt F = m a τ = rf τ = I α KE = 1 2 mv 2 KE R = 1 2 I ω2 p = m v L = r p L = I ω Jerry Gilfoyle The Arctic and the Length of Day 9 / 42
14 Which One Wins? A wooden disk and a metal ring have the same mass m and radius r and start from rest and roll down an inclined plane (see figure). What are the kinetic energies at the bottom in terms of the height of the incline h, m, r, and any other constants? Which one is going faster at the bottom of the incline and gets to the bottom in the shortest time? v r v d h Jerry Gilfoyle The Arctic and the Length of Day 10 / 42
15 Moments of Inertia Jerry Gilfoyle The Arctic and the Length of Day 11 / 42
16 Linear Rotational Quantities Linear Rotational Quantity Connection Quantity s s = rθ θ = s r v T v T = rω ω = v T r = dθ dt a a T = rα α = a T r = dω dt F = m a τ = rf τ = I α KE = 1 2 mv 2 KE R = 1 2 I ω2 p = m v L = r p L = I ω Jerry Gilfoyle The Arctic and the Length of Day 12 / 42
17 Rolling Down an Incline - 1 Jerry Gilfoyle The Arctic and the Length of Day 14 / 42
18 Rolling Down an Incline - 2 Rolling Down an Incline 40 y HpixelsL Jerry Gilfoyle x HpixelsL 20 The Arctic and the Length of Day / 42
19 Which One Wins? A wooden disk and a metal ring have the same mass m and radius r and start from rest and roll down an inclined plane (see figure). What are the kinetic energies at the bottom in terms of the height of the incline h, m, r, and any other constants? Which one is going faster at the bottom of the incline and gets to the bottom in the shortest time? v r v d h Jerry Gilfoyle The Arctic and the Length of Day 17 / 42
20 Rolling Jerry Gilfoyle The Arctic and the Length of Day 20 / 42
21 Linear Rotational Quantities Linear Rotational Quantity Connection Quantity s s = rθ θ = s r v T v T = rω ω = v T r = dθ dt a a T = rα α = a T r = dω dt F = m a τ = rf τ = I α KE = 1 2 mv 2 KE R = 1 2 I ω2 p = m v L = r p L = I ω Jerry Gilfoyle The Arctic and the Length of Day 22 / 42
22 Torque - Rotational Force The shield door at a neutron test facility at Lawrence Livermore Laboratory is possibly the world s heaviest hinged door. It has a mass m = 44, 000 kg, a rotational inertia about a vertical axis through its hinges of I = kg m 2, and a (front) face width of w = 2.4 m. A steady force F a = 72 N, applied at its outer edge and perpendicular to the plane of the door, can move it from rest through an angle θ = 90 in t = 30 s. What is the torque exerted by the friction in the hinges? If the hinges have a radius r h = 0.1 m what is the friction force? Jerry Gilfoyle The Arctic and the Length of Day 24 / 42
23 Torque - Rotational Equivalent of Force Airplane String Jerry Gilfoyle The Arctic and the Length of Day 25 / 42
24 Torque - Rotational Equivalent of Force Airplane Side View Top View Pivot String F a θ Airplane R h Pivot r a θ a Propeller Radius r a Jerry Gilfoyle The Arctic and the Length of Day 25 / 42
25 Torque - Rotational Equivalent of Force Airplane Side View Top View F String a Pivot θ Airplane R h Pivot r a r a θ a F f Propeller Radius r a Jerry Gilfoyle The Arctic and the Length of Day 25 / 42
26 Torque - Rotational Equivalent of Force F = m a τ = r F F Jerry Gilfoyle The Arctic and the Length of Day 26 / 42
27 Linear Rotational Quantities Linear Rotational Quantity Connection Quantity s s = rθ θ = s r v T v T = rω ω = v T r = dθ dt a a T = rα α = a T r = dω dt F = m a τ = rf τ = I α KE = 1 2 mv 2 KE R = 1 2 I ω2 p = m v L = rp L = I ω Jerry Gilfoyle The Arctic and the Length of Day 27 / 42
28 Rotational Form of F = m a Rotator Disk Applied torque Jerry Gilfoyle The Arctic and the Length of Day 28 / 42
29 Torque and Rotational Energy - An Application A trebuchet is a device used in the Middle Ages to throw big rocks at castles and is now used to throw other things like pumpkins, pianos,... Consider the figures below. The trebuchet has a stiff wooden beam of mass m b = 15 kg and length l b = 5 m with masses m c = 700 kg (the counterweight) and m p = 0.1 kg (the payload) on it s ends. Treat these two masses as point particles. A frictionless axle is located a distance d = 0.15 m from the counterweight. The beam is released from rest in a horizontal position. We will launch the payload from a bucket at the end of the beam. What is the maximum speed the payload can reach before it leaves the bucket? Jerry Gilfoyle The Arctic and the Length of Day 29 / 42
30 Angular Momentum y p p φ p r x Jerry Gilfoyle The Arctic and the Length of Day 31 / 42
31 Twirling Student A student volunteer/victim is spinning around on a turntable with her arms outstretched. She is spinning initially at a rate of ω 0 and then drops her arms flat to her side at a distance r b from the axis. Treat the student s body as a cylinder of mass m b and radius r b with thin rods for arms of length l a and mass m a. The turntable has a moment of inertia of I t. What is her final rotation rate ω 1 in terms of the quantities listed above? Arms Body Turntable Rotation Axis Jerry Gilfoyle The Arctic and the Length of Day 33 / 42
32 Moments of Inertia Jerry Gilfoyle The Arctic and the Length of Day 34 / 42
33 Linear Rotational Quantities Linear Rotational Quantity Connection Quantity s s = rθ θ = s r v T v = rω ω = v r = dθ dt a a = rα α = a r = dω dt F = m a = d p dt τ = rf τ = I α = d L dt KE = 1 2 mv 2 KE R = 1 2 I ω2 p = m v L = rp L = I ω Jerry Gilfoyle The Arctic and the Length of Day 35 / 42
34 Angular Momentum Conservation Jerry Gilfoyle The Arctic and the Length of Day 36 / 42
35 Angular Momentum Conservation Lab - Inputs To get the movie or data file go to the following website ggilfoyl/genphys/131/links2.html right-click on the appropriate link and save it to the Desktop. disk diameter m weight diameter m mass of disk 5.10 kg mass of weight 1.0 kg I of rotator kg m 2 center-to-edgeof-weight m Jerry Gilfoyle The Arctic and the Length of Day 37 / 42
36 Melting Ice - Rotating Earth - 1 Consider a model of the Earth consisting of a uniform sphere of water with a thin, circular ice cap at the North Pole symmetric about the rotation axis. Treat the ice cap as infinitely thin and sitting on top of the water. If the ice melts, the water is evenly distributed over the all-ocean Earth. The initial ice cap mass is m 1 = kg, its surface mass density is σ = kg/m 2, and its angular size is θ 1 = 13.0 (see figure). The density of water is ρ water = 10 3 kg/m 3. The moment of inertia of the ice cap is I c = (8/3)πσR 4 E (2 + cos θ 1 ) sin 4 (θ 1 /2) where R E is the Earth s radius. Let the initial mass of the Earth m E be just the water part and not include the Arctic ice cap. Your high-precision clock can detect changes in the LOD as small as ms (1 ms = 10 3 s). θ Jerry Gilfoyle The Arctic and the Length of Day 38 / 42
37 Melting Ice - Rotating Earth What is the initial moment of inertia I E1 of the water-only part of the Earth? 2 What is the initial moment of inertia I C1 of the ice cap? 3 The ice cap melts, θ shrinks by 0.1 and its mass drops by m = kg. How much does the added water change the radius of the Earth? 4 How much does I E of the Earth change? 5 How much does I c of the ice cap change? 6 What happens to the LOD after the melting? 7 Should NSF fund you? θ Initial ice cap mass m 1 = kg Ice cap angle 1 θ 1 = 13.0 Surface mass density σ = kg/m 2 Ice cap angle 2 θ 1 = 12.9 Mass loss m = kg Water density ρ w = 10 3 kg/m 3 Jerry Gilfoyle The Arctic and the Length of Day 39 / 42
38 Should NSF Fund You? 1 Annual change in LOD from Arctic ice melting is 20 µs. Jerry Gilfoyle The Arctic and the Length of Day 41 / 42
39 Should NSF Fund You? 1 Annual change in LOD from Arctic ice melting is 20 µs. 2 The resolution of the proposed instrument is 5 µs. Jerry Gilfoyle The Arctic and the Length of Day 41 / 42
40 Should NSF Fund You? 1 Annual change in LOD from Arctic ice melting is 20 µs. 2 The resolution of the proposed instrument is 5 µs. 3 Is the signal big enough to detect? Jerry Gilfoyle The Arctic and the Length of Day 41 / 42
41 Should NSF Fund You? 1 Annual change in LOD from Arctic ice melting is 20 µs. 2 The resolution of the proposed instrument is 5 µs. 3 Is the signal big enough to detect? 4 What is the background? International Earth Rotation and Reference Systems Service data. Jerry Gilfoyle The Arctic and the Length of Day 41 / 42
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