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Motion and Forces

LETS START WITH MOTION

- How can you prove that an object is moving?

MOTION

- Motion- An object is in motion when the distance

from another object is changing. - Reference Point- A place or object used for

comparison to determine if something is in

motion. - An object is in motion if it changes position

relative to a reference point.

CALCULATING SPEED

- Speed Distance / Time
- If you measure distance in meters and time in

seconds you express speed in m/s - Give an example of the speed a snail could

travel. - Constant speed-When the speed of an object does

not change - Average speed- Total distance / total time

MOTION

- Velocity- Speed and direction
- Acceleration- Rate at which velocity changes

(increasing speed, decreasing speed, changing

direction) m/s/s - EXAMPLES OF ACCELERATION???
- Accelerationfinal velocity- initial velocity /

time

Acceleration problems

- Suppose a car moving in a straight line steadily

increases its speed each second, first from 35 to

40 km/hr, then from 40 to 45 km/hr, then from 45

to 50 km/hr. What is its acceleration?

Acceleration problems continued

- In 5 seconds a car moving in a straight line

increases its speed from 50 km/hr to 65 km/hr

while a truck goes from rest to 15 km/hr in one

second. Which undergoes the greatest

acceleration? What is the acceleration of each

vehicle?

Think about this

- The Cat bus is approaching Lone Mountain at 144

cm/s. A person on the bus is facing forward and

walking 36 cm/s relative to everything in the

bus. The person is eating a hotdog which is

entering his mouth at 2 cm/s. An ant on the

hotdog is running away from the persons mouth at

1cm/s. How fast is the ant approaching Lone

Mountain?

NEWTONS FIRST LAW OF MOTION

- Law of Inertia
- An object at rest will remain at rest and an

object that is moving will continue moving unless

acted upon by an unbalanced force. - What do you think an unbalanced force is?

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Unbalanced Force

UNBALANCED FORCE

- Unbalanced forces cause an object to start

moving, stop moving, or change direction. (an

unbalanced force will cause an object to

accelerate) - Net force- The overall force on an object after

all the forces are added together

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BALANCED FORCES

- Balanced forces are equal forces acting in an

opposite direction. - Balanced forces do not cause acceleration.

A force is just a push or a pull

MOMENTUM!!!

- Mass x Velocity Momentum (P)
- Increase the mass or the velocity to get more

momentum.

Conservation of Momentum

- Newtons Balls (Newtonian Demonstration)
- Pool Table

NEWTONS SECOND LAW OF MOTION

- Force, Mass, and Acceleration

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UNITS

- Mass- kg which equals 1000 grams (g)
- Acceleration- m/s/s
- Force- kg x m/s/s or Newton (N)
- SAMPLE PROBLEM
- A 52 kg water-skier is being pulled by a

speedboat. The force causes her to accelerate at

2m/s/s. Calculate the net force that causes this

acceleration.

FRICTION

- Friction- The force that one surface exerts on

another when the two rub against each other. - Two factors- Type of surface and how hard they

rub together. - Sliding friction- dry solid surfaces
- Rolling friction- rolling over a surface
- Fluid friction- object moves through a liquid or

gas.

LAW OF UNIVERSAL GRAVITATION

- Law of universal gravitation states that the

force of gravity acts between all objects in the

universe. - The strength of the force depends on the masses

of the objects and the distance from them

GRAVITY

- Free fall- when the only force acting on a

falling object is gravity. (9.8m/s/s) - Do all objects regardless of mass fall at this

rate? (water cup demo) - What about projectiles?

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GRAVITY

- Air resistance- a type of fluid friction that

objects falling through air experience. - Paper vs.. Book
- Weight- The measure of the force of gravity on an

object (scale) - Mass- is a measure of the amount of matter in

that object.

WEIGHT DUE TO GRAVITY

- Remember Fma???
- Weight mass x acceleration due to gravity
- Weight mass(kg) x 9.8 m/s/s
- The amount of force you apply to the ground in

Newtons

NEWTONS THIRD LAW OF MOTION

- ACTION AND REACTION

EVERY ACTION HAS AN EQUAL AND OPPOSITE REACTION!!!

3rd law only refers to forces on 2 different

objects

What about circular motion???

- Bucket Demonstration
- What is the centripetal force for a satellite?
- Centripetal- center seeking
- Centripetal force- any force that causes an

object to move in a circle.

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