**Motion, Forces & Energy**

**What is Motion?**

**Chapter Review**

**What is Acceleration?**

Motion can be described by distance, speed, displacement, and velocity, where displacement and velocity also include direction.

Acceleration occurs whenever an object speeds up, slows down, or changes direction.

Inertia is the tendency of an object to resist a change in motion. Momentum is related to how hard it is to stop the object.

The law of conservation of momentum states than in a collision, the total momentum of the objects that collide is the same before and after the collision.

**THE UNIVERSE**

The Solar System

Earth

**What is Motion?**

**A. All matter is constantly in**

MOTION

.

MOTION

.

**B. Motion involves a**

CHANGE

in position.

CHANGE

in position.

**1. An object changes position relative to a**

REFERENCE

point.

REFERENCE

point.

**2.**

DISTANCE

is the total length of the route an object travels when it moves.

(scalar quantity - size but not direction)

DISTANCE

is the total length of the route an object travels when it moves.

(scalar quantity - size but not direction)

**3.**

DISPLACEMENT

includes distance and direction of the stopping point from the starting point.

(vector quantity - has a size and direction)

DISPLACEMENT

includes distance and direction of the stopping point from the starting point.

(vector quantity - has a size and direction)

C.

SPEED - a measure of how quickly something moves.

1. The formula for

SPEED

can be written as: speed = distance/time. (OR v(speed) = d/t)

2. The units of speed are units of distance

divided by units of time; in SI units, speed is given as

METERS PER SECOND

(m/s).

Q: If a car has traveled 50 meters in 5 seconds; how fast was it going?

3. An object in motion can change

SPEED

many times as it moves from one point to another, speeding up or slowing down.

a.

AVERAGE SPEED

is the total distance traveled divided by the total time taken.

b. An object's speed at a particular moment in time is called

INSTANTANEOUS SPEED

.

c.

CONSTANT

speed occurs when an object travels at a steady rate with the same instantaneous speed for some period of time.

D. Motion can be

GRAPHED

on a distance-time graph with time plotted on the horizontal axis and distance plotted on the vertical axis.

CONSTANT SPEED INCREASE

CONSTANT SPEED

CONSTANT SPEED DECREASE

1. The steeper the line on a distance-time graph, the greater the

SPEED

.

2. A horizontal line on a distance-time graph indicates that no change in

POSITION

is occurring, and the speed is

ZERO

.

E.

VELOCITY

- speed of an object and its direction of motion; velocity changes if either, or both, of these changes.

Last Launch of Space Shuttle Endeavour

A.

ACCELERATION

- change in velocity divided by the time for the change to occur; it can include an object speeding up, slowing down, and/or changing direction.

B. Acceleration can be

CALCULATED

if you know how an object's velocity has changed during a given time period.

1. The formula for calculating

ACCELERATION

is:

Acceleration = final speed - initial speed / time or

a = (v-u)/t

.

can be rearranged to calc. final speed

v= u + at

a. The unit of acceleration is distance divided by time squared; in SI units, acceleration is given as

METERS PER SECOND SQUARED

(m/s2)

.

b. Acceleration is

POSITIVE

when an object speeds up and

NEGATIVE

when an object slows down.

Positive Acceleration (Speeding up)

No Acceleration

(Constant Speed)

Negative Acceleration (Slowing down)

2. Acceleration can be

GRAPHED

with speed on the vertical axis and time on the horizontal axis.

a. An object that is speeding up will have a line on a speed-time graph that slopes

UP & RIGHT

.

b. An object that is slowing down will have a line on a speed-time graph that slopes

DOWN & RIGHT

.

c. A horizontal line would indicate acceleration of

ZERO

, or constant speed.

**What is Momentum?**

A. The amount of matter in an object is its mass;

MOMENTUM

is the tendency of an object to resist a change in its motion.

Object filled with matter

B. MOMENTUM

- measure of how hard it is to stop an object; calculated as mass times velocity.

1. With

MOMENTUM

expressed as p, the equation can be written as: p = mv

2. Momentum

INCREASES

if the mass or velocity of the object increases.

3. Momentum has direction that is the same direction as its velocity.

C.

CONSERVATION OF MOMENTUM

- the total momentum of objects that collide with each other does not change.

1. There are

MANY

ways collisions can occur.

a. In one type, objects stick together and

MOVE

still stuck together.

b. In another type, two objects bounce off each other when they collide, and may transfer

MOMENTUM

from one to another.

2. In both cases, the

TOTAL

momentum of the objects that collide is the same before and after the collision.

Pre-quiz:

1. describe a situation in which a feather and a hammer would fall at the same rate

2. describe displacement

3. define force

4. state what quantity each of the following instruments measure

a) speedometer

b) trip meter

5. state what quantity is measured in each of the following units

a) m/s

b) kilometres

c) newtons

speed in km/h

speed in m/s

divide 3.6

multiply 3.6

Distance calculations

1. an object is travelling at 15 m/s for 10 seconds.

d = vt

2. an object is travelling at 20 m/s for 15 minutes. How far does it travel?

3. Trinh rides her bike with a constant speed of 5m/s. It takes her 3 minutes to get to the milk bar. Calculate how far away it is.

4. While Trinh is riding, a toddler runs onto the road ahead. If Trinh took 0.5 secs to react, how far does she travel before hitting the road?

Speed calculations

1. convert the following speeds into km/h

a) 3m/s

b) 12.5 m/s

2. convert the following speeds into m/s

a) 54 km/h

b) 16.2 km/h

3. Theo spent 8 hours travelling 400 km from his home in Bundaberg to visit his sister in Toowoomba. Calculate Theo's average speed for the journey.

C. Velocity

- how displacement changes with time

1. The formula for

Velocity

can be written as: velocity = distplacement/time. (OR v(speed) = d/t)

2. The units of speed are units of distance

divided by units of time; in SI units, speed is given as

METERS PER SECOND

(m/s).

Q: If a car has traveled 50 meters in 5 seconds; how fast was it going?

average acceleration and final speed

1. a car speeds up to 60 km/h from rest in 5 seconds. calculate its average acceleration (km/h/s)

2. a train initially travelling at 30 km/h accelerates at a constant rate of 2 km/h/s for 30 seconds. Calculate it's final speed.

3. a car brakes from a speed of 30 m's decelerating at a rate of -5 m's. Calculate time taken to stop and eventual speed.

fill in the missing values

use the acceleration formula to calc. missing values

Practice makes perfect

acceleration due to gravity

a falling object accelerates towards earth because of the force of gravity.

acceleration due to gravity is 9.8 m/s2 (1 g)

speed of object increases by 9.8 m/s (or 36km/h) for every second it falls

G-force

air resistance

- the friction between air and a falling object

terminal velocity

- the final velocity

Human tolerance

depends on how big the force, duration, direction, part of body they affect.

can handle horizontal better then vertical

forces experienced in vertical drop are dangerous as blood flow to the brain can be disrupted

body can withstand momentary force but longer durations can be deadly

vertical dives up to 300 km/h

as it pulls out of a dive,

the falcon can withstand

forces up to 25g!