Motion Chapter 11

Motion Motion is changing position against a fixed point. You can tell if something is moving if its position changes against some background that stays the same (frame of reference). Displacement is the change in position of an object.

Motion Speed describes how fast an object moves (scalar). Velocity describes the speed of an object plus the direction in which it is moving (vector). Example: Tina the Llama escaped at a speed of 4.5 m/s. Tina the Llama escaped at a velocity of 4.5 m/s to the north.

Motion Calculating speed and velocity: v = d / t velocity or speed distance time

Motion The cheetah, the fastest of land animals, can run a distance of 274 m in 8.65 s at its top speed. What is the cheetah’s top speed? v = d= t = ? v = d / t 274 m v = 274 m / 8.65 s 8.65 s V = 31.7 m/s

Motion Suppose the polar bear were running on land instead of swimming. If the polar bear runs at a speed of about 29,880 m/h, how far will it travel in 10.0 hours? v = d= t = 29,880 m/h t * v = d / t * t ? d = v * t 10 h d = 29,880 m/h * 10 h d = 298,800 m

Motion The various types of tree sloths share the honor of being the slowest-moving mammals. An average tree sloth moves with a speed of 0.743 m/s. How long does it take a sloth moving at this speed to travel 22.30 m? v = d= t = 0.743 m/s t * v = d / t * t 22.30 m v * t = d v v ? t = d / v t = 22.30 m / 0.743 m/s t = 30.0 s

Motion Speed can be shown on a distance-time graph. The slope of the line on this graph will be equal to the speed.

Acceleration Acceleration is any change in velocity (vector). When is an object accelerating? Speeds Up (positive accel), Slows Down (negative accel or deceleration), or changes direction

Acceleration Calculating acceleration: a = v / t v = vf – vo change in velocity time v = vf – vo Change in velocity = final velocity – initial velocity Units for Acceleration: Velocity units/time units (you will have 2 time units) Ex: m/s/s or m/s2

Acceleration Acceleration can be shown on a velocity-time graph. The slope of the line on this graph will be equal to the acceleration.

An inline skater traveling in a straight line goes from 3 m/s to 9 m/s in 3s. What is the acceleration? Δv = vf – vo Δv = 9 m/s – 3 m/s Δv = 6 m/s t= 3s a = 6 m/s / 3s a = 2 m/s/s or 2 m/s2

Acceleration a = Δv= = t = ? a = v / t a = 15 m/s / 4.04 s vf – vo The gravitational force between Mars and an object near its surface is much lower than the force between an object on Earth’s surface and Earth. If a dropped hammer’s speed increases from 0.0 m/s to 15.0 m/s in 4.04 s, what is the acceleration due to the gravitational force on the surface of Mars? a = Δv= = t = ? a = v / t a = 15 m/s / 4.04 s vf – vo a = 3.713 m/s2 15.0 m/s – 0.0 m/s 15.0 m/s 4.04 s

Acceleration A bicyclist accelerates at 0.89 m/s2 during a 5.0 s interval. What is the change in the speed of the bicyclist and the bicycle? a = Δv= t = 0.89 m/s2 Δv = a * t Δv = 0.89 m/s2 * 5.0 s ? Δv = 4.5 m/s 5.0 s

Acceleration An automobile accelerates 1.77 m/s2 over 6.00 s to reach freeway speed at the end of an entrance ramp. If the car’s final speed is 24.44 m/s, what was its initial speed when it began accelerating? a = Δv= t = 1.77 m/s2 Δv = a * t Δv = 1.77 m/s2 * 6 s ? Δv = 10.62 m/s 6 s Δv = vf - vo 10.62 = 24.44 - vo vo = 24.44 m/s – 10.62 m/s vo = 13.8 m/s