11.3 Acceleration

1-31-11

YOU SHOULD HAVE NOTES OUT TO TURN IN. I’LL BE GIVING THESE BACK TO KEEP FOR STUDYING FOR SEMESTER FINAL EXAM.

You should have completed and turned in the following labs IN BOX:

1) motion detector lab - 4 sketched activity graphs and 8 questions (including 2 with graphs)

2) 50-yd/100-yd football race activity including tables and example calculations including slope of best-fit-lines as well as 2 graphs (distance-time and velocity-time graphs)... Pre-AP should also have calculations for instantaneous acceleration.)

3) computer lab activities

STRIKES will count on field trip if not in the box today. Strikes marked tomorrow.Complete the Notes for new unit on forces Parts A, B, & C (all of this presentation.)

12.1 Forces

Watch motion using strobe light video to see a special effect on motion...

QuickTime™ and a decompressor

are needed to see this picture.

12.1 Forces

The wind pushes against the man and his umbrella. The push from the wind is a force.

12.1 Forces

How do forces affect the motion of an object?A force is a push or a pull that acts on an object.

A force can cause a resting object to move, or it can accelerate a moving object by changing the object’s speed or direction.

What Is a Force?

12.1 Forces

Measuring ForceYou may have measured forces using a spring scale. The stretch of the spring in the scale depends on the amount of weight (a type of force) acting on it.

What Is a Force?

12.1 Forces

Units of ForceOne newton (N) is the force that causes a 1-kilogram mass to accelerate at a rate of 1 meter per second each second (1 m/s2).

1 N = 1 kg•m/s2

What Is a Force?

12.1 Forces

Representing ForceArrows can represent a force. The lengths of the arrows show relative amounts of force.

What Is a Force?

12.1 Forces

When the forces on an object are balanced, the net force is zero, and there is no change in the object’s motion.

Combining Forces

When an unbalanced force acts on an object, the object accelerates.

How do forces affect the motion of an object? SHOW “FORCE” VISUAL WITH MY.HRW.COM PS HOLT CH.11 FORCES.

http://www.my.hrw.com

12.1 Forces

The net force is the overall force acting on an object after all the forces are combined.

• Forces in the same direction add together.• Forces in opposite directions subtract from one another.

Combining Forces

12.1 Forces

Balanced ForcesBalanced forces are forces that combine to produce a net force of zero, and there is no change in the object’s motion.

An unlimited number of individual forces can act on an object to produce a net force of zero.

Combining Forces

12.1 Forces

The two groups pull with equal forces in opposite directions. The forces combine to make a net force of zero. (tug-a-war example, arm wrestling...equal - no movement)-

Combining Forces - EXAMPLES

12.1 Forces

Unbalanced ForcesAn unbalanced force is a force that results when the net force acting on an object is not equal to zero. When an unbalanced force acts on an object, the object accelerates. Example - Winning of the tug-a-war team...

optional video:

http://videos.howstuffworks.com/hsw/7949-newtons-laws-third-law-of-motion-video.htm

Combining Forces

12.1 Forces

Forces can add together or subtract from one another.

Combining Forces

Adding forces

12.1 Forces

Forces can add together or subtract from one another.

Combining Forces

Adding forces Subtracting forces

12.1 Forces

Forces can add together or subtract from one another.

Combining Forces

Adding forces Subtracting forces

Equal and opposite forces

12.1 Forces

What are the four main types of friction?Friction is a force that opposes the motion of objects that touch as they move past each other.

Without friction, we would not be able to write, walk, drive, catch a ball, etc.

Friction

There are four main types of friction: static friction, sliding friction, rolling friction, and fluid friction.

12.1 Forces

Static FrictionStatic friction is the friction force that acts on objects that are not moving.

Static friction always acts in the direction opposite to that of the applied force.

Examples: push a book at rest...

Friction

12.1 Forces

Sliding FrictionSliding friction is a force that opposes the direction of motion of an object as it slides over a surface.

Sliding friction is less than static friction.

Example: pushing a moving book or moving pot...

Friction

12.1 Forces

A. Static friction–the potted tree does not move.

B. Sliding friction–when the tree moves, sliding friction acts to oppose the direction of motion.

Friction

12.1 Forces

Rolling FrictionRolling friction is the friction force that acts on rolling objects.

The force of rolling friction is about 100 to 1000 times less than the force of static or sliding friction.

Friction

12.1 Forces

Ball bearings in these wheels greatly reduce friction by replacing sliding friction with rolling friction. (other example - dollies...)

Friction - EXAMPLES Rolling Friction

12.1 Forces

Fluid Friction• Fluid friction opposes the motion of an object

through a fluid (including liquids & gases). • Fluid friction increases as the speed of the

object moving through the fluid increases. • Examples: Stirring cake batter, swimming,

driving a car...

Friction

12.1 Forces

• Fluid friction acting on an object moving through the air is known as air resistance.

• Examples: parachutes, driving cars, wind suits, etc.

12.1 Forces

Complete Stations 1-5 of the Motion in Our World Lab...

Brainstorm your ideas on the egg drop project with group of 3...

Get approval for idea and start bringing supplies...Record your first ideas on the laptop...

Send me your group members and the computer and log-in information in case your partner is absent... via my e-mail... I’ll only open these if I need to get a computer up with project...

We will be using iMovie...