USV: Physical Science: Forces

A push or a pull How can you tell

those objects are exerting a force on each other?

What are other examples of forces?

Forces are measured in NEWTONS (N)

1N is the force needed to change the speed of a 1-kg object by 1m/s

Measure with a spring scale

Discuss with your table partner situations you encountered today where you saw evidence of a forces being exerted.

Be sure to describe the source of the force.

Give at least two examples.

UNBALANCED FORCE = movement of an object An object at rest will move A moving object will

change or stop BALANCED FORCE =

equal forces acting in opposite directions that causes no change in motion

Combinations of forces will determine the effect of forces

NET FORCE = combination of all forces acting on the object

A. 100 N upB. 100 N downC. 20 N upD. 20 N down

60 N

40 N

A. 150 N upB. 150 N downC. 90 N upD. 90 N downE. 30 N upF. 30 N down

60 N

40 N

50 N

Force between surfaces that resists the movement of one surface past the other surface Ice skates on ice Tires and the road

Rougher surface = more friction

Rolling – resists the motion of a rolling object

Sliding – resists the motion of a sliding object

Static – resists the motion of an object

Good: Feet & ground Wheels & ground Keeps you on the

scooter Bad:

Wind and soil = erosion Causes heat that can

make engines run less efficiently

Can wear things down

Force of attraction that exists between any two objects

Pull of gravity depends on1. MASS of object greater mass = greater gravitation force

MASS = amount of matter in an object

2. The closer the centers of the two objects are, the greater the force

Which of the following has more pull of gravity?

5 kg

10 kg

10 kg

5 kg

15 m

15 mA.

B.

Which of the following has more pull of gravity?

5 kg 5 kg

20 m

15 m

5 kg5 kg

A.

B.

Pages 430-431 Gravity determines

the motion of the planets and stars

The moon’s gravity causes the tides in Earth’s oceans Moon pulls the water

away from the Earth on one side & pulls Earth away from water on the other side

The moon affects the tides more than the sun does because…A. The sun is closer to the Earth than the

moonB. The sun is more massive than the moonC. The moon is closer to the Earth than the

sunD. The moon is more massive than the sun

Imagine that you live on Mars. The gravity is about ½ of our gravity here on Earth. Write a description of how the reduced gravitational force would affect your everyday activities. This should be interesting!

FRAME OF REFERENCE = the object an observer uses to detect motion Seat on a roller

coaster The sun Your mailbox

What are the different frames of reference in this

picture?

RELATIVE MOTION = the change in position of one object compared to the position of another object So, we can’t feel that

we are moving 1600 km/hour due to the Earth’s rotation because the Earth is moving too!

What does looking at the sun tell us?

3 TYPES OF MOTION Vibrational = rapid

back and forth movement – drum cymbals

Circular = motion around a central point – yo-yo

Straight line = motion in a line

1. Eardrum gathering sound

2. Bike wheel3. Speakers4. Walking5. Movement of a planet6. Cars driving7. Violin strings

A. CircularB. Straight

lineC. Vibration

al

SPEED = the distance an object moves in a certain period of time Speed = distance/time

INSTANTANEOUS SPEED = speed at any given point Checked with a

SPEEDOMETER VELOCITY = a measure of

both the speed and direction of a moving object 10 meters per seconds north

ACCELERATION = the change in velocity during a particular time period Speeding up Slowing down Changing direction

Results from unbalanced forces acting on the object

Speed= distance ÷ time Distance = speed x time Time = distance ÷ speed

How long would it take me to travel 20m on my bike if I my speed was 5 m/hr?

A. 25 hrB. 100 hrC. 4 hr

1660’s English scientist LAW = statement that

describes events or relationships that exist in nature

Newton formed laws based on experiments & observations about how things move in ideal conditions

Objects resist changes in motion Object at rest stays

at rest unless acted on by an unbalanced force

Object in motion continues in motion unless acted on by an unbalanced force

INERTIA = the tendency of an object to resist any change in its state of motion More mass = more

inertia

What is it like in outer space?

Why do we wear seat belts?

An object’s acceleration depends on the mass of the object and the size and direction of the force acting on it.

Force = mass x acceleration

I would need to exert a large force to move a large mass

I would need to exert a small force to move a small mass

Objects accelerate in the direction of the force that acts on them

As acceleration is changing, force must also be changing

You are riding on a bicycle. You stop to place a heavy object on the back of the bike. How will the increased mass affect the bike’s acceleration if you pedal with the same force?A. It will decreaseB. It will stay the sameC. It will increase

When a force is applied to an object, the object exerts an equal force in the opposite direction

Law of action and reaction

440

Depends on its mass and velocity

The more momentum an object has, the harder it is to stop

Momentum is transferred when objects collide

           

Law of Conservation of Momentum says that momentum before the collision is equal to momentum after the collision

           

Which has greater momentum, a car sitting still or a pebble rolling down a hill?A. CarB. Pebble

An adult and a child are ice skating. The child pushes away from the adult. The child moves backward. What will happen to the adult?A. NothingB. The adult will move in the same direction

as the childC. The adult will move in the opposite

direction from the child

You apply a force to a soccer ball when you kick it. Compare this force to the force that the soccer ball exerts on your foot.A. The soccer ball exerts a weaker

force on your foot in the opposite direction

B. The soccer ball exerts the same force on your foot in the opposite direction

C. The soccer ball exerts a weaker force on your foot in the same direction