Energy
Part 2
Fundamental relationships &
definitions
• Energy is the ability to cause change (damage)
• We’ll focus on Mechanical Energy, which
includes: KE + PEg + PEs.
• We’ll ignore non-mechanical energies, such as
nuclear, chemical, and “internal” (atomic kinetic).
• Fundamental relationship:
the energy of a system only changes if
outside influences act on the system.
• DME = S Wext + Qext + lightext. We’ll ignore last
two terms for now.
Start here Monday 7/20/09
Which will be moving faster at the bottom of the
string when a ball is released at the height
equivalent to a 20 degree arc?
3
2
25
1. Ball falling in a circular arc
2. Ball falling straight down
3. Both are the same
Where does it have more ME?
1.
2.
3.
4.
0
0
0
0
Tie
Location2
Loc. 3
Placeholder in case need 4
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
When is it faster?
1
9
17
1. On way up
2. On way down
3. Same
When is it faster?
2
5
24
1. On way up on left
2. On way up on right
3. Same
Y1 = 0 on incline with spring
1. True
2. false
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
Yc =
1
26
0
1
0
1.
2.
3.
4.
5.
8cm cos 10
8 cm sin 10
-8cm cos 10
-8 cm sin 10
8 cm