The physics of movement

 Kinematics is the science of describing the motion of objects using words, diagrams, numbers, graphs, and equations.  In this lesson, we will investigate the words used to describe the motion of objects. That is, we will focus on the language of kinematics.

 We will study such terms as:  Scalars  Vectors  Distance  Displacement  Speed  Velocity  Acceleration.

 The terms used to describe motion can be broken down into two categories:  Scalar are quantities that are fully described by a numerical value alone.  Vector are quantities that are fully described by both a numerical value and a direction.

A. 5 m Scalar B. 30 m/sec East Vector C. 5 mi., North Vector D. 20 degrees Celsius Scalar E. 256 megabytes Scalar F CaloriesScalar To test your understanding of this distinction, consider the following quantities listed below. Categorize each quantity as being either a vector or a scalar.

your home your school A displacement has Size = length of this arrow displacement from home to school To go to school from home... size & direction.

Distance = length of path you travelled (  size of displacement) l1l1 l2l2 l3l3 To go to school from home... your home your school = l 1 + l 2 + l 3

There is a distinction between distance and displacement. Displacement (blue line) is how far the object is from its starting point, regardless of how it got there. Distance traveled (dashed line) is measured along the actual path.

©2008 by W.H. Freeman and Company Left: Displacement is positive. Right: Displacement is negative. The displacement is written:

How fast is it really going?

 Speed is generally used to describe how fast something happens, but it is defined as ‘the rate at which an object moves over distance, over a variable amount of time’.  Speed has a variety of units depending on the units used for distance and time.

 average speed = distance  time  distance = average speed x time  time = distance  average speed Note: 1 kilometre (km) = 1000 metres

Distance TimeSpeed Example: If you are working out distance you cover the word distance and you know the equation is: average speed x time

1. Speed = a. Distance (9000 m) ÷ Time (12.12 seconds) = m/s 2. Speed= a. Distance (528 m) ÷ Time (4 seconds) = 132 m/s 3. Distance = a. Average Speed (96 m/s) × Time (17 seconds) = 1632 m 4. Time = a.Distance (500, 000m) ÷ Average Speed (700 m/s) = s Speed Distance Time

5. Time = a. Distance (350 km) ÷ Speed (80km/hr) = hrs 6. Time = a. Distance (450 km or 450,000m) ÷ Speed (120 m/s) = 3750 s 7. Speed = a. Distance (1km or 1000m) ÷ Time (20 minutes or 1200 s) = 0.83 m/s 8. Distance = a.Average Speed (6 m/s) × Time (3 minutes or 180 s) = 1080 m

9. Distance = a.Average Speed (100 km/hr or 27.7m/s*) × Time (10 minutes or 600 s) = 10. Time = a.Distance (20 km or 20,000m) ÷ Average Speed (40 m/s) = 500 s 100 km/hr 100,000 m/hr 1666 m/min 27.7 m/s *Conversion Covert to meters Covert to meters per minute 100km x ,000 ÷60 Covert to meters per second 1666 ÷60 Conversion complete

Distance vs. Time Graphs

 average speed = distance  time  distance = average speed x time  time = distance  average speed Remember calculations involving speed involve: Distance Time

The wolf started from his house. Travelled to the straw house. Stayed to blow it down and eat dinner. Travelled to the stick home. Again, stayed to blow it down and eat dinner. Travelled to the brick house. Dies in the stew pot at the brick house.

a)How many stops does the boat make? b)What is the boat’s average speed for the whole trip? c)What is the highest speed the boat reaches?

Constant Accelerating at 1m/s/s No Acceleration Increasing Acceleration Deceleration

 Acceleration refers to the speeding up or slowing down.  Deceleration (retardation) refers to a negative acceleration.  Technically, acceleration is change of velocity with respect to time. Acceleration = change in speed time

 A motorist gets in her car & accelerates up to 60km/h in 5s. What is her average acceleration?  Note: generally the SI unit for acceleration is m/s/s. Activity: Acceleration Calculations Acceleration = change in speed time = final speed – initial speed time = (60 – 0)km/h 5 s = 12km/h/s or 12km/h s -1 If answer was negative, then this would be deceleration.

1.A car changes its velocity by 30 m/s in 5 seconds, what is the acceleration of the car? 2.A bike starts from rest and accelerates to 20 m/s over a period of 6 seconds. What is the acceleration of the car? 3.A man moving at 2 m/s accelerates at a rate of 3 m/s 2 for 2.5 seconds. What is the new velocity of the man? 4.A car decelerates from 60 m/s to 20 m/s at a rate of -5 m/s 2. How long does this deceleration take the car? 6 m/s m/s m/s 8 seconds

 Acceleration directed toward the center of circular path

To every action there is always an equal and opposite reaction

What would happen if you tried to push a desk while on a skateboard?

For every action there is an equal and opposite re-action. What Does this mean? For every force there is a reaction force that is equal in size, but opposite in direction. That is to say that whenever an object pushes another object it gets pushed back in the opposite direction equally hard. Can you explain how action-reaction forces are involved in the following pictures?

As the rocket flies up through space, exhaust exits from the back of the rocket. The exhaust acts on the rocket pushing it upwards. The rocket has an equal and opposite action on the exhaust, expelling it downwards.

 The man acts on the shopping cart, propelling it forward. The shopping cart acts on the man’s hands, pushing back on his hands with a reaction that he can feel. However, while he feels a force pushing him backwards the man does not actually move backwards, since he can overcome that force with his feet and legs.

As the dolphins swim through the water, they act on the water, pushing it aside and backwards. The water exerts an equal and opposite reaction on the dolphins, propelling them forward. Action Reaction

The hammer acts on the nail, driving it into the wood. The nail acts on the hammer, pushing back on the head of the hammer with a reaction that can be felt by the hand holding the hammer. As the nail is driven into the wood, the nail acts on the wood, but the reaction force of the wood on the nail is unbalanced, allowing the nail to accelerate into the wood.

 Interpret the following types of graphs: ▪ Displacement vs. Time ▪ Speed (velocity) vs. Time ▪ Acceleration vs. Time  Be able to use the following ▪ average speed = distance  time ▪ distance = average speed x time ▪ time = distance  average speed  Calculate Acceleration: Remember to use the triangle Acceleration = change in speed time = final speed – initial speed time