Locomotion in a physical world
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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. Components to describe motion. Position = 0. Position = 1.

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Locomotion in a physical world

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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


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.


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”


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.


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.


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?


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.


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


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


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.


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


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?


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


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.


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


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.


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


  • 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?


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.


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.


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