Changes in speed Part 8.2

Who accelerates faster? Pagani Zonda 0-100 km/hour in just 3.5 seconds The Cheetah, has the ability to accelerate from 0 to 100 kilometers per hour in just three seconds. Bugatti Veyron Super Sport: 0–100 km/h in just 2.5 seconds

Calculating acceleration http://www.one-school.net/Malaysia/UniversityandCollege/SPM/revisioncard/physics/forceandmotion/linearmotion.html

Calculating acceleration of cheetah and cars

The car is speeding up as it moves toward the right The car is speeding up as it moves toward the right. It therefore has positive acceleration in our coordinate system. This car is slowing down as it moves toward the right. Therefore, it has negative acceleration in our coordinate system, because its acceleration is toward the left. The car is also decelerating: the direction of its acceleration is opposite to its direction of motion. (c) This car is moving toward the left, but slowing down over time. Therefore, its acceleration is positive in our coordinate system because it is toward the right. However, the car is decelerating because its acceleration is opposite to its motion. (d) This car is speeding up as it moves toward the left. It has negative acceleration because it is accelerating toward the left. However, because its acceleration is in the same direction as its motion, it is speeding up (not decelerating).

The Rev is driving his car, when suddenly the engine stops working The Rev is driving his car, when suddenly the engine stops working! If he is travelling at 10 ms-1 and his decceleration is 2 ms-2 how long will it take for the car to come to rest? v = u + at t = 5 seconds http://www.physicsforidiots.com/dynamics.html

The horizontal straight line shows something that is moving with a constant velocity. Straight lines slanting upwards show objects whose velocity is increasing at a steady rate – they have constant positive acceleration. Straight lines slanting downwards show objects whose velocity is decreasing at a steady rate – they have a constant negative acceleration (retardation). The steeper the line the greater the acceleration or retardation. A curved line shows an object whose acceleration is changing as time goes by. http://www.schoolphysics.co.uk/age14-16/Mechanics/Motion/text/Velocity_time_graphs/index.html

(a) Motion diagram for a car moving at constant velocity (zero acceleration). (b) Motion diagram for a car whose constant acceleration is in the direction of its velocity. The velocity vector at each instant is indicated by a red arrow, and the constant acceleration by a violet arrow. (c) Motion diagram for a car whose constant acceleration is in the direction opposite the velocity at each instant.

Prac p. 268

Acceleration due to gravity

No Air resistance

WITH Air resistance http://www.physicsclassroom.com/mmedia/newtlaws/efar.cfm

Human tolerances depend on the magnitude of the g-force, the length of time it is applied, the direction it acts, the location of application, and the posture of the body. The human body is flexible and deformable, particularly the softer tissues. A hard slap on the face may briefly impose hundreds of g locally but not produce any real damage; a constant 16 g for a minute, however, may be deadly. When vibration is experienced, relatively low peak g levels can be severely damaging if they are at the resonance frequency of organs and connective tissues. To some degree, g-tolerance can be trainable, and there is also considerable variation in innate ability between individuals. In addition, some illnesses, particularly cardiovascular problems, reduce g-tolerance.

Vertical axis g-force: Aircraft, in particular, exert g-force along the axis aligned with the spine. This causes significant variation in blood pressure along the length of the subject’s body, which limits the maximum g-forces that can be tolerated. In aircraft, g-forces are often towards the feet, which forces blood away from the head; this causes problems with the eyes and brain in particular. As g-forces increase a Brownout can occur, where the vision loses hue. If g-force is increased further tunnel vision will appear, and then at still higher g, loss of vision, while consciousness is maintained. This is termed “blacking out”. Beyond this point loss of consciousness will occur, sometimes known as “G-LOC” (”loc” stands for “loss of consciousness”). Beyond G-LOC, if g-forces are not quickly reduced, death can occur. While tolerance varies, with g-forces towards the feet, a typical person can handle about 5 g (49m/s²) before g-loc, but through the combination of special g-suits and efforts to strain muscles—both of which act to force blood back into the brain—modern pilots can typically handle 9 g (88 m/s²) sustained (for a period of time) or more (see High-G training). Resistance to “negative” or upward g’s, which drive blood to the head, is much lower. This limit is typically in the −2 to −3 g (−20 m/s² to −30 m/s²) range. The subject’s vision turns red, referred to as a red out. This is probably because capillaries in the eyes swell or burst under the increased blood pressure. Horizontal axis g-force: John Stapp was subjected to 15 g for 0.6 second and a peak of 22 g during a 19 March 1954 rocket sled test. The human body is better at surviving g-forces that are perpendicular to the spine. In general when the acceleration is forwards, so that the g-force pushes the body backwards (colloquially known as “eyeballs in”) a much higher tolerance is shown than when the acceleration is backwards, and the g-force is pushing the body forwards (”eyeballs out”) since blood vessels in the retina appear more sensitive in the latter direction. Early experiments showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes without loss of consciousness or apparent long-term harm.[10] The record for peak experimental horizontal g-force tolerance is held by acceleration pioneer John Stapp, in a series of rocket sled deceleration experiments in which he survived forces up to 46.2 times the force of gravity for less than a second. Stapp suffered life-long damage to his vision from this test. But do not worry if you fly with us as we fly according to G tolerance, and you may experience up to 6Gs max!

Graphing acceleration

Measure and calculate acceleration

The small variation of the acceleration due to gravity with latitude means that the weight of a 100 kg person depends on their location on Earth. At all three locations the person's weight is 980 N (and g=9.8 m s−2) to two significant figures.