Locomotion in a Locomotion in a physical worldphysical 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 Components to describe motionmotion

• Change in position– Change in distance (d)

– Change in time (t)Final distance – initial distance = distance or d

Final time – initial time = time or t

Position = 0 Position = 1

Change in position at 1 cm/ second

Moved for 1 second.

• How would you describe that the ball moved back to its original position?

Components to describe Components to describe motionmotion

Final distance – initial distance = distance

Position = 0 Position = 1

1 cm − 0 cm = − 1.0 cm

Change in position at − 1 cm/ second

Moved for 1 second. Including direction is “velocity”velocity”

Speed and velocitySpeed 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.

MeasurementMeasurement

• 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 A common sense approach: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?

AccelerationAcceleration• 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?

• 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.

Now that we’ve described components of motion Now that we’ve described components of motion can you tell me what causes motion or can you tell me what causes motion or movement?movement? FORCE!

Inertia?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?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

The ball sitting on the table? Yes; uniform motion

The moon orbiting around the earth? Yes; uniform motion

Rush hour traffic? Not uniform motion

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 Change in motion due to unbalanced forces – unbalanced forces –

Newton’s 2Newton’s 2ndnd Law Law• How can we calculate Force?

• F = m*a• unit of measure = Newtons (N) 1 N = 1 kg m

s2

Why include mass for force?

Mass affects inertia – an objects tendency to resist a change in motion

a = accleration due to gravity = 9.8 m/s2

What happens if a large object What happens if a large object encounters a force generated by a encounters a force generated by a

smaller object?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 Why does the ball stop?stop?

• If the ball pushes on the table; does the table push back?

• Identify forces– Are the forces balanced?

Force = m a

Acceleration due to gravity = 9.8 m / s2

Force applied by my hand

If you were standing on the ball and If you were standing on the ball and took a step off which direction would took a step off which direction would

the ball be directed?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 One last thing to consider: What is consider: What is

friction?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 What you should be able to do: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.