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Motion and Forces

MOTION

S8P3. Students will investigate relationship

between force, mass, and the motion of objects.

a. Determine the relationship between velocity

and acceleration.

How are forces and motion related?

- A force is a push or a pull that can result in

motion. - When a force has been applied to an object and

the object moves, work is being done.

How can motion be described?

- By using a reference point A (usually)

stationary object that helps you detect the

motion of an object. (Ex. tree, house etc.)

- Once the reference point is determined you can

define motion by speed, position, and direction.

What is speed?

- Speed refers to how fast an object travels. (Rate

at which an object moves.) - Depends on
- Distance
- Time

- Various forms of speed
- Instantaneous speed at a given moment

(speedometer) - Constant speed that doesnt change (cruise

control) - Changing speed that varies (running a mile)

- Average speed used when objects are not moving

at a constant rate. - Formula
- Speed distance
- time

- Ex. If you ran the distance of a football field

(91 meters) in 30s, would you run the same speed

from start to finish? - No, you find the average speed you ran.

- s d/t
- s 91m
- 30s
- 3.03 m/s

How can you graph speed?

Make up a scenario about what's taking place for

each line on the graph

Two cars traveled at 50 km/h on the same highway.

After 2 hours the cars are 200 km away from each

other. How is this possible?

THEY HAVE DIFFERENT VELOCITIES

What is velocity?

Would you rather know the hurricanes speed or

velocity?

- Velocity speed of an object in a particular

direction. - Velocity changes when speed or direction of an

object changes. - Unit would look like 5 m/s NW

Can you have a constant speed but a changing

velocity?

- Yes, the Ferris wheel can be moving at a constant

speed but its constantly changing direction!

How is acceleration related to velocity?

- Acceleration rate of change of speed (velocity)
- Occurs when an object changes
- Speed
- Direction
- Both

What are the types of acceleration?

- Positive Acceleration speeding up
- Negative Acceleration slowing down

How do you find acceleration?

- Formula
- a vf vi
- t

What are velocity/time graphs?

- Shows change in velocity over time (acceleration).

Moving at a constant velocity

Moving at a positive acceleration velocity

changing at constant rate.

Moving at a negative acceleration velocity

changing at constant rate.

What is centripetal acceleration?

- Acceleration that occurs in a circular motion

object traveling in a circle is constantly

changing directions so acceleration occurs

continuously

FORCES

- S8P3. Students will investigate relationship

between force, mass, and the motion of objects. - b. Demonstrate the effect of balanced and

unbalanced forces on an object in terms of

gravity, inertia, and friction.

What is a force?

- A force is a push or pull that one body exerts on

another. - Ex. Friction, gravity, kicking a football.
- Unit Newton (N)

What is a net force?

- The sum of the forces acting on an object.

What is a balanced force?

- When the forces acting on the object are equal in

size and opposite in direction. - Net force 0 (forces cancel each other out)
- No change in motion occurs!!

What is an unbalanced force?

- Occurs when forces acting on the object are

unequal. - Net Force is in the direction of the larger

force. (object will move in that direction)

What is the difference between balanced and

unbalanced forces?

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What is Inertia?

- The tendency of an object to resist change.

Which has a greater inertia?

- Elephant inertia depends on mass!!

What is Newtons 1st Law of Motion state?

- An object in motion will stay in motion unless an

outside force acts upon it. - An object at rest will stay at rest unless an

outside force acts upon it.

What is another name for the 1st Law?

- The Law of Inertia

What is the relationship between force, mass, and

acceleration?

Force and Acceleration

- The greater the force applied to an object the

greater the acceleration will be.

Force and Mass

- Acceleration will be less on a object that is

heavier. - Ex. Softball v. Baseball

What does Newtons 2nd Law state?

- An object will accelerate in the direction of the

net force. - F m x a, a F/m,
- m F/a

What is the unit for force?

- Newton
- kg x m/s/s

Types of Forces

What is a force that opposes motion between 2

moving objects?

- FRICTION

What does the amount of friction depend on?

- 1.Kind of surface
- 2. Force pressing surfaces together.

What is static friction?

- Friction between two surfaces that are not moving

past one another.

What is sliding friction?

- Force that opposes motion of 2 objects sliding

past one another.

What is Rolling Friction?

- Opposing motion between two objects rolling past

each other.

How is friction helpful?

- Without friction the tires could not push against

the ground to move the car forward and brakes

couldnt stop the car.

How can you reduce friction?

- Lubricants are used to reduce friction.
- Ex. Motor oil, wax, grease
- Switching from sliding to rolling friction
- Ex. Ball bearings between wheel axles

- S8P5. Students will recognize characteristics of

gravity, electricity, and magnetism as major

kinds of forces acting in nature. - a. Recognize that every object exerts

gravitational force on every other object and

that the force exerted depends on how much mass

the objects have and how far apart they are.

What is Gravity?

- A downward force
- Any 2 masses exert an attractive force on each

other. - Strength of gravitational force depend on
- 1.) Mass
- 2.) Distance

What is the law of universal gravitation?

- All objects are attracted to each by

gravitational force. - The larger the object The greater the force
- The closer together the object the greater the

force.

Is weight a force?

- Weight is considered to be a gravitational force

that decreases as you move from Earth.

How can you find weight?

- F m x a
- W m x 9.8 m/s/s

What is the difference between mass and weight?

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- Mass how much matter makes up an object
- (Doesnt change as you move from the Earth to the

moon.) - Weight considered to be a gravitational force
- (Decreases as you move from the Earth to the

moon.)

What is acceleration due to gravity?

- Anything that falls through the air falls at an

acceleration of 9.8m/s/s.

What is Air Resistance?

- Effects anything that is in Earths atmosphere.
- Upward force that opposes gravity of anything

falling through the air.

Air Resistance Depends on 3 things

- 1. SPEED
- 2. SIZE
- 3. SHAPE
- of an object.

- If there were no air resistance a hammer and

feather would fall at the same time.

What is a projectile?

- Anything that is thrown or shot through the air.

Why do projectiles follow a curved path?

- They follow a curved path due to pull of gravity.
- Ex An arrow, Bullet, Basketball

What is Newtons 3rd Law of Motion?

- When one object exerts a force on a second

object, the second one exerts a force that is

equal and in size and opposite in direction. - Action/Reaction Occurs

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What is Momentum?

- Momentum is related to how much force is needed

to change an objects motion. - Momentum mass x velocity
- p m x v

What is the law of conservation of momentum?

- Momentum can be transferred from one object to

another

What is the relationship between mass and

velocity?

- If two trucks have same velocity, but different

masses then . . . - the truck with the larger mass has more momentum