Lecture 17 - Force and Motion

Question 1

what are the 4 attributes of a vector?

Answer 1

1. magnitude (speed)
2. direction (heading)
3. point of application (CoG)
4. line of action

Question 2

what is the difference between velocity and speed?

Answer 2

• velocity is a vector
• speed is scalar
• velocity is the rate of change with respect to time (how long it takes to get from point a to b)

Question 3

what is average velocity?

Answer 3

• (s2-s1)/(t2-t1)
• delta s / delta t
• measured in m/s or km/hr
• assuming she is running at a constant speed
• measure s1 and s2 very close together (to avoid change of speed problems)

Question 4

what is instantaneous velocity?

Answer 4

• when you measure s1 and s2 where dt = 0
• v = ds/dt
• in m/s or km/h
• we lose no information, this tells us our expact speed at that time

Question 5

why is measuring average velocity over an entire race not an accurate measurement of speed?

Answer 5

• acceleration and deceleration phase are not accounted for
• deceleration will occur after ~70m (or you are not reaching max speed)

Question 6

what is cyclic velocity?

Answer 6

• the average velocity if an activity is cyclic
• ex: running, swimming, etc.
• v = distance per cycle x (# cycles/minute)

Question 7

what is acceleration vs negative acceleration?

Answer 7

• acceleration = speeding up
• negative acceleration = slowing down

Question 8

what is average acceleration?

Answer 8

• a = delta v / delta t
• unit = m/s^2
• instantaneous velocity at two different times

Question 9

what is instantaneous acceleration?

Answer 9

• instantaneous velocity at two times that are infinitesimally close together
• a = dv / dt
• unit = m/s^2

Question 10

how does gravity contribute to acceleration?

Answer 10

• always acting on the body’s COG
• g = 9.81m/s^2
• aka speeding up by 9.81m/s every second of falling

Question 11

how is force of gravity related to weight?

Answer 11

• proportional
• no matter what size, the object will fall at the same pace

Question 12

what is terminal velocity?

Answer 12

• free-falling at a constant acceleration of g
• drag increases as speed increases
• acceleration is zero, speed is constant (for terminal)
• stop of acceleration because speed is constant

Question 13

why does velocity have a parabolic motion?

Answer 13

• vertical component is always accelerating downwards at g
• horizontal component is constant
• these components behave differently

Question 14

what is newton’s 2nd law for constant mass?

Answer 14

• F = ma
• as force increases, acceleration will also increase assuming mass stays the same

Question 15

what is newton’s 2nd law for constant force?

Answer 15

• if force is the same, the more massive object will have a smaller acceleration

Question 16

what is newton’s 2nd law for constant acceleration?

Answer 16

• if acceleration is the same, the more massive object requires more force to be applied

Question 17

what is newton’s 3rd law?

Answer 17

• an equal and opposite reaction that acts on the other body
• muscles create the action, reaction from the ground/surrounding causes the motion
• to accelerate forwards we push backwards
• to slow down we push forwards
• to turn left we push rights (and vice versa)

Question 18

what is the human tolerance to acceleration?

Answer 18

• blood in the body is mobile, will move in the body with acceleration
• need to avoid negative g’s for too long (positive g’s headward and footward, negative backward and footward)