Locomotion in a physical world

1. Locomotion in a physical world • Most animals have some form of locomotion which separate them from plants and fungi • What is motion? • A natural event that involves change in the position or location of an object or organism

2. Components to describe motion Position = 0 Position = 1 • Change in position • Change in distance (d) • Change in time (t) Final distance – initial distance = D distance or Dd Final time – initial time = D time or Dt Change in position at 1 cm/ second Moved for 1 second.

3. Components to describe motion • How would you describe that the ball moved back to its original position? Position = 0 Position = 1 Final distance – initial distance = D distance 1 cm − 0 cm = − 1.0 cm Change in position at − 1 cm/ second Moved for 1 second. Including direction is “velocity”

4. Speed and velocity • Velocity is a measure of the speed in a given direction. • e.g. You can say the top speed of an airplane is 300 kilometers per hour (kph). But its velocity is 300 kph in a northeast direction. • Speed is how fast an object is going with respect to an object. • e.g. You can say that you travel in your car at 70 miles per hour (mph). But your velocity is………? • We distinguish between speed and velocity because if you add the speeds of objects, their directions are important. • For example, the velocity of an airplane with respect to the ground would vary according to the direction of the wind.

5. Measurement • In order to determine how fast an object is going, you measure the time it takes to cover a given distance. Its velocity (v) or speed equals the distance (d) traveled divided by the time (t) it takes to go that distance: v = d / t • For example, if a car went 120 miles in 2 hours, its average speed would be the distance of 120 miles divided by the time of 2 hours equaling 60 miles per hour (mph). • IAvg. Velocity Va = (Vi + Vf) / 2 • If you travel from Milwaukee to Chicago (90 miles) at an average velocity of 60 mph, it would take you 90 mi. / 60 mph = 1.5 hours to travel the distance.

6. A common sense approach: • If a ball starts at the 30cm mark and travels at a velocity of 10cm/sec for 3 seconds, stops, then travels at a velocity of - 5cm/sec for 2 seconds, where will it end up?

7. Acceleration • Acceleration is the increase of velocity over a period of time. Deceleration is the decrease of velocity. • e.g. When you start running, you accelerate (increase your velocity) until you reach a constant speed. • A = Vf - V I change in velocity over time t When you are moving is your velocity always the same? Acceleration is a way to describe these changes in velocity.

8. A ball starts with a velocity of 0 m/sec, then accelerates smoothly and reaches the 1 meter mark in 10 seconds. What is the acceleration of the ball? 1 m

9. What is the velocity of the ball after 5 seconds of the calculated acceleration?

10. Now that we’ve described components of motion can you tell me what causes motion or movement? FORCE! • Newton’s 1st Law of motion: Inertia • Every object retains its state of uniform motion unless acted upon by an unbalanced force. • An object at rest remains at rest. • An object in motion will continue in a straight line at a constant velocity.

11. Inertia? • a body at rest tends to stay at rest and a body in motion tends to stay in motion unless acted upon by an unbalanced force

12. Uniform motion? • Changing position in a constant and unvarying manner. • What does this mean----identify if the following would be an example of uniform motion Yes; uniform motion The ball sitting on the table? Yes; uniform motion The moon orbiting around the earth? Not uniform motion Rush hour traffic? Can you think of forces that act upon a ball sitting on a table? Rolling across the floor? Being lifted from the table?

13. Change in motion due to unbalanced forces – Newton’s 2nd Law • How can we calculate Force? • F = m*a • unit of measure = Newtons (N) 1 N = 1 kg m s2 a = accleration due to gravity = 9.8 m/s2 • Why include mass for force? • Mass affects inertia – an objects tendency to resist a change in motion

14. What happens if a large object encounters a force generated by a smaller object? • Newton’s Third law of Motion • Whenever 2 objects interact, the force exerted on one object is equal to and in the opposite direction of the force exerted on the other object.

15. Why does the ball stop? • If the ball pushes on the table; does the table push back? • Identify forces • Are the forces balanced? Force applied by my hand Force = m a Acceleration due to gravity = 9.8 m / s2

16. If you were standing on the ball and took a step off which direction would the ball be directed? • The force you would exert might exceed the capacity for the ball to resist a change in motion. • You push the ball backward and the result is an opposite reaction of your motion (force) directed forward.

17. A 50 kg person takes a single step. She accelerates her body at 1m/s2. How much force is involved?

18. Now, think of yourself walking….do you exert a force in the direction you are moving, or do you exert a force in the opposite direction? (Hint: Newton’s 3rd law) • So, if the person is on firm ground, and given that the earth weighs 5.98*1024 kg, how much does she accelerate the ground?

19. One last thing to consider: What is friction? • Friction results from the two surfaces being pressed together closely, causing intermolecular attractive forces between molecules of different surfaces. • As such, friction depends upon the nature of the two surfaces and upon the degree to which they are pressed together.

20. What you should be able to do: • Manipulate and solve algebraic equations and problems involving position, speed, velocity, acceleration, mass and force. • Identify the units of each of these quantities. • Compare speed and velocity. • Explain how friction and gravity affect motion, and be able to use this in problem solving. • Identify forces acting on an object and determine whether they are balanced or unbalanced. • Identify and use Newton’s 3 Laws of Motion to explain the general properties of motion.