Unit 2 Forces & Motion

Unit 2 Forces & Motion

Unit Review

​Describing Motion

• Motion happens when an object changes position over time.

• ​Speed is how fast something is changing its position.

  • ​Speed = distance/time

  • ​Speed units = m/s

• ​Velocity is speed WITH direction.

  • ​represent with + or -

  • represent with direction (North, South, East, West)

Multiple Choice

Velocity is speed with __________________________.

• a unicycle helmet

• direction

• fight

Multiple Choice

A change in ________ in a certain amount of time is motion.

• speed

• appearance

• position

• weight

Multiple Choice

A vehicle travels 2345 m in 315 s toward the evening sun. What is its speed?

• 7.44 m/s

• 0.13 m/s

• 738,675 m/s

• 7.44m

​Acceleration

• The rate at which velocity changes.​

• ​Speed may increase.

• ​Speed may decrease.

• ​There may be a change in direction.

• ​acceleration = velocity/time

• ​a = v/t

• ​m/s² = m/s/s

Multiple Choice

Why does a car accelerate as it round a corner at a constant speed?

• Its direction changes
• It doesn't
• It slows down
• Its speeds up  

Multiple Choice

A box sliding down an inclined plane attains a velocity of 27 m/s in 3 seconds from rest.  Find the acceleration.

• 30 m/s
• 24 m/s²
• 9 m/s²
• 81 km/hr

Multiple Choice

Acceleration only takes place when things speed up. 

• True
• False

Force = Push or Pull​

Multiple Choice

What is a force?

• A push

• A pull

• A pull or a push

• An energy

​Contact Force

• ​A force that involves physical contact.

• ​Friction - objects rubbing together

• ​Elastic - such as a spring, rubber band, or bouncy ball

• ​Fluid - such as objects floating on water.

• ​Tension - pulling on something like a rope

​Noncontact Force

• a force that does not involve physical contact.

• ​Gravitational - the pull of gravity.

  ​Electromagnetic - the force between two charged particles.

• ​Intermolecular - forces that hold molecules (like H₂O) together.

• ​Nuclear - forces that hold subatomic particles (protons, neutrons, & electrons) together.

Multiple Choice

what kind of force is represented in the picture by

$$\overrightarrow{f}$$  

• gravitation force

• electric force

• magnetic force

• friction force

Multiple Choice

what is the force shown in the picture?

• magnetic force

• electric force

• applied force

Multiple Choice

What force holds the planets in motion around the sun?

• Magnetic
• Electrical
• Gravitational
• Air Resistance

​Newton's First Law of Motion

• An object in motion will stay in motion unless acted upon by an external force.

• An object at rest will stay at rest unless acted upon by an external force.

• Called the "Law of Inertia."

• ​Inertia = an object's resistance to change its motion.

• ​More mass = more inertia

Multiple Choice

The tendency of an object to resist a change in its state of motion is called the object's ______.

• incline
• straight line
• friction 
• inertia 

Multiple Choice

Objects at rest remain at rest and objects traveling at a steady rate in a straight line continue that way until a _________acts on them.  

• force
• velocity
• inertia
• acceleration 

​Newton's Second Law of Motion

• Force = Mass time Acceleration

  • F = m*a

  • ​Force units = Newton (N)

  • ​Mass units = kilograms (kg)

  • Acceleration units = m/s²

  ​Momentum is the quantity of motion of a body/object.

• ​Momentum = mass times velocity

  • ​Momentum units = kg*m/s

  • ​Mass units = kg

  • ​Velocity units = m/s

Multiple Choice

Acceleration is caused by a force acting on a mass.

• Newton’s first law of motion
• Newton’s second law of motion
• Newton’s third law of motion

Multiple Choice

A 20 kg bike accelerates at 10 m/s².  what was the force?

• 25 Newtons
• 20 Newtons
• 200 Newtons
• 10 Newtons

Multiple Choice

A force of 250 N is applied to an object that accelerates at a rate of 5 m/s².  What is the mass of the object? To solve this problem you must do - 

• 250 ÷ 5
• 5 ÷ 250
• 250 x 5

​Newton's Third Law of Motion

• Every action has an equal, but opposite, reaction.

• Every force has an equal, but opposite, force.

• A net force is needed to move an object.​

Multiple Choice

When you push on a wall, the wall pushes on you.

• True

• False

Multiple Choice

Which best explains why we are able to accelerate forward when starting to run?

• As one leg moves backward, it provides an equal and opposite force for the other foot to move forward.
• No acceleration takes place. Runners are always at a fixed velocity.
• The striking foot pushes backward against the ground. The friction with the ground provides an equal and opposite force forward.
• The runner's upper body quickly leans forward, causing the entire body to begin accelerating forward

​Gravity

• Gravity is the force one object exerts on another.

• ​Weight is the pull of gravity on an object.

  • ​Mass is how much matter an object has and is NOT affected by gravity.

• ​The planets stay in orbit because of gravity.

• ​Gravity is responsible for star and planet formation.

• ​Gravity causes acceleration.

• ​Escape velocity is the velocity an object must have to break away from earth's gravitational field.

• ​Gravity is different on different planets.

Multiple Choice

The ____ of an object is the force of gravity on the object.

• mass
• weight
• volume
• density

Multiple Choice

You can think of it as "how much stuff makes up an object"

• size
• brightness
• mass
• density

Multiple Choice

In order to break free of a planet's gravity, an object must be moving faster than the _____

• escape velocity
• getaway acceleration
• break-away pace
• liberation altitude

Multiple Choice

In space you have the same mass as you do on Earth, but no _____

• microgravity
• weight
• density
• pressure