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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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