Chapter 11 motion_power_point

CHAPTER 11 MOTION

SECTION 11.1 DISTANCE AND DISPLACEMENT

11.1 DISTANCE AND DISPLACEMENT

All of science is concerned with motion.

The motion of objects change when forces act upon them.

All objects have motion they just appear to be motionless. All of matter contains atoms that are continuously in motion (vibrate and collide).

In order to describe motion you must state the direction in which the object is moving and how fast the object is moving.

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You have to choose a frame of reference. ( To describe motion accurately)

It is a system of objects that are not moving with respect to one another.

EX. People on the bus are not a good frame of reference because they are moving with the bus. You need to choose and object not moving outside the bus.

You have to choose an appropriate frame of reference to describe motion in a clear and relevant manner.

Relevant Motion is movement in relation to a frame of reference.

MEASURING DISTANCE

Distance is the length of a path between two points.

SI unit for distance is the meter (m)

However, for larger distances it is better to use kilometers (km)

MEASURING DISPLACEMENTS

Displacement is the direction from the starting point and the length of a straight line from the starting point to the ending point.

Displacement use vectors

A vector is a quantity that has magnitude and direction.

Magnitude can be the size, length, or amount of something.

Arrows on maps represent vectors.

Symbol for vector →

COMBINING DISPLACEMENTS

Distance: Displacements along a straight line

Use vector addition or subtraction.

Going 10 km east and 3 km west = 10-3 = 7

Page 330 demo

Use vector addition if in a straight line 4km + 2km = 6km

DISPLACEMENT THAT ISN’T ALONG A STRAIGHT PATH

Resultant vector- is the vector sum of two or more vectors.

The vector goes directly from the starting point to the end point.

P. 331 Figure 4

SECTION 11.2 SPEED AND VELOCITY

Speed- is the ratio of the distance an object moves to the amount of time the object moves.

SI unit = m/s*use the units that make the most sense.

cars = miles/hr or km/hr

2 Ways to express the speed of an object

1. Average speed- (v) is the total distance traveled, (d) divided by the time, (t) it takes to travel that distance.

CALCULATING SPEEDFormula:

Average speed = Total distance v = d

Total time t

Sometimes you have to rearrange the formula to solve for distance or time.

d = v × t t = d

v

• The speed of the object can change during the time it moves but, this equation gives you the overall average.

11.2 SPEED AND VELOCITY

Instantaneous Speed (v) is the rate at which an object is moving at a given moment in time.

Ex driving car look at a speedometer.

• Average speed is computed for the duration of a trip. And it does not have to be the speed that you are driving throughout the whole trip. Instantaneous is JUST the speed at a particular moment

11.2 SPEED AND VELOCITY

Velocity is the speed and direction in which an object is moving (has to be measured relative to a reference point)

• calculated the same as speed

• It is a vector (use an arrow.)

Combining Velocities

Use vector addition when the motion involves more than one velocity ( direction).

Example:

Boat Velocity with respect to river bank is the same directions with the water at 12 km/hr.

River is moving 5km/h

How fast is the boat moving? Answer: 5km/h + 12 km/h = 17 km/h

11.2 SPEED AND VELOCITY

In vector addition you add the speed of water and the speed of the boat.

5km/h + 12 km/h = 17 km/h

Example 2:

When the boat is moving opposite of the flow of the water.

Velocity with respect to river bank is the same directions against the water at 12 km/hr.

Answer: 5km/h - 12 km/h = 7 km/h You subtract the movement of the boat from the movement of the water.

11.3 ACCELERATIONAcceleration - the rate at which velocity changes.

• Unit m/s2 Meters per second squared.

• Velocity changes all the time.

• You can have positive or negative acceleration.

Negative is slowing down and decreases acceleration

Positive is speeding up and increases acceleration.

11.3 ACCELERATION

Acceleration can be described as changes in speed, changes in direction, or changes in both speed and direction.

• It is a vector.

1. Change in speed = free fall

Ex: parachuting before you engage the chute.

Movement of an object towards the Earth solely because of gravity.

Value of acceleration due to gravity = 9.8 m/s2

Speed is m/s

Acceleration is m/s2

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2. Change in direction

- You are still accelerating but your speed is constant.

Ex:

riding bike around a curve (you coast)

Carousel ( merry-go-round)

3. Change in direction and speed

Ex:

roller coaster

car around a curve ( slowdown)

11.3 ACCELERATION

Constant Acceleration

• Is a steady change in velocity.

• The velocity of the object changes by the same amount each second.

Ex: Jet taking off. Constantly accelerating

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How to calculate acceleration

• Assume that we are moving in a straight line of motion- divide the change in velocity by the total time

Formula : Acceleration = Change in velocity

Total Time

A= (vf-vi) f= final, i= initial

T