ForcesMs. Fezza

Physical Science

Miami Arts Charter

Motion Practice Problems1. A motorcycle has a mass of 250 kg and a velocity of 68 m/s, what is it’s

momentum?

2. A truck travels to and from a stone quarry that is located 2.5 km to the east. What

is its distance? What is its displacement?

3. A cross-country runner runs 10 km in 40 minutes. What is his average speed?

4. A dog travels 250 meters east in 8 seconds. What is the velocity of the dog?

Problems continued 4. A 10-kg wagon has a speed of 25 m/s. What is its momentum?

5. A dog travels north for 18 meters, east for 8 meters, south for 27 meters and then

west for 8 meters. What is the distance the dog traveled and what is the displacement

of the dog.

6. Brittany drove at a speed of 85 km / hr south for 4 hours. How far did she travel?

7. What is the mass of an object that has a force of 89 N and an acceleration of 25

m/s2?

Momentum Review Problem1. A large truck loaded with scrap steel weighs 14,000 kg and is traveling north on

the interstate heading for Chicago. It has been averaging 48 hm/h for the journey

and has traveled over 1450 km so far. It has just stopped to refuel. What is its

current momentum?

a. 672,000

b. 1866.66

c. 18666.66

d. 6720

Plickers ProblemJames rode his bike 0.65 hours and traveled 8.45 km. What was his speed?

a. 3.61 m/s

b. 36.1 m/s

c. 5.4925m/s

d. 549.25m/s

ForceForce: A push or pull that changes an object’s state of motion or causes the object to

deform. Force is measured in the SI unit of Newtons (N).

Some forces are obvious, some are not

Forces cause the motion of an object to change

-The velocity is changed by the applied force

Net Force: the sum of all the force acting on an object when there are two or more

forces acting on an object

Forces have a magnitude and direction, therefore it is a ___________.

Fundamental ForcesGravitational Force- Attraction of two masses

Electromagnetism- Holds atoms together. Works on all charged particles.

Strong Nuclear- Holds the nucleus of an atom together

Weak Nuclear Forces- Radioactive Decay

ForceForce = Mass x Acceleration

F= ma

SI Unit is Newtons

Unbalanced and Balanced ForcesIf the net force has a non-zero value, the object moves. This is the result of unbalanced

forces

Balanced forces are when the same size force is being applied in opposite directions. The

net force of the object is zero. (Equal in size, opposite direction) No change in motion

Isaac Newton

- Cambridge University

- 1665 at 23 years old he developed the Law of Universal Gravitation, calculus, and

the three laws of how forces affect motion.

- https://www.youtube.com/watch?v=PCxP24qj2UQ

Newton’s Laws1st Law: An object moves at constant velocity unless an unbalanced force acts on it.

(An object at rest stays at rest until acted on by an unbalanced force)

-Also known as the law of Inertia

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

Ex: When a car stops and your body keeps moving forward.

Amount of inertia is related to the amount of mass the object has

2nd Law: An object’s acceleration is in the same direction as the net force of the object.

The Force of the object is equal to the mass of the object and the acceleration.

F= ma

3rd Law: To every action is an equal and opposite reaction. When one object exerts a

force on a second object, the second object exerts a force on the first object that is

equal in strength and opposite in direction.

Friction- Force that opposes the sliding motion of two surfaces that are touching.

- When two surfaces are in contact, welding or sticking occurs when the surfaces

touch, a force must be applied to break the microweld or sticking.

- The amount of friction depends on the surface and the force pressing the surfaces

together.

Types of Friction- Static Friction is the force that prevents two surfaces from moving past one

another. (due to the microwelds that have formed between the two surfaces)

- Kinetic friction opposes the motion of two surfaces sliding past one another.

Normally smaller that static friction.

- Rolling Friction static friction working over the area that is touching which causes

a motion. The static friction keeps the wheel from slipping. This allows the wheel

to propel forward or backward.

Units of Motion *Test 10/27-10/28Momentum = kgm/s

Acceleration = 5 m/s

2

Velocity = m/s

Force = Newtons (N)

Distance = meters (m)

Time = seconds (s)

Weight = Newtons (N)

Mass = kilograms (kg)

Quizlet Sfezza

Units

Practice Problems * Math Test 10/31 - 11/11. A force of 20 N acts upon a 5 kg block. Calculate the acceleration of the object.

2. An object of mass 300 kg is observed to accelerate at the rate of 4 m/s2. Calculate

the force required to produce this acceleration.

3. A 5 kg block is pulled across a table by a horizontal force of 40 N with a frictional

force of 8 N opposing the motion. Calculate the acceleration of the object.

4. An object of mass 30 kg is in free fall in a vacuum where there is no air resistance.

Determine the acceleration of the object.

5. An object of mass 30 kg is falling in air and experiences a force due to air resistance

of 50 newtons. What is the acceleration of the object. (use the problem above)

6. A student pushes on a crate with a force of 100 N directed to the right. What force

does the crate exert on the student?

7. A force of 200 N is exerted on an object of mass 40 kg that is located on a sheet of

perfectly smooth ice.

8. For a person who has a mass 60 kg, calculate the weight in newtons.

9. An object of mass 10 kg is accelerated upward at 2 m/s2. What force is required?

Early Astronomy- Used the sky for navigation, predicting seasons and mythological, cosmological,

calendrical, and astrological beliefs

- Early Astronomy had many attempts to describe and explain the motion of the

stars and planets, but they were unsatisfactory

Geocentric Universe- Geocentric means “earth-centered”

- Credited to Ptolemy

- Alexandrian Greek

- 100 A.D.

- Very old

- Incorrect

- Fit the observational data, but very

Complicated

Visualizing Ptolemy's Universe- https://www.youtube.com/watch?v=EpSy0Lkm3zM

Heliocentric Model of the Universe- Copernicus

- Polish Cleric

- Sun centered model of the universe

- 1500s

- Incorrect because Earth is not the center of the universe, but the center of our

solar system.

Objections- How could Earth be moving at enormous speeds if we don’t feel it?

- Why can’t we detect Earth’s motion against the background stars? (Stellar

Paradox)

- Copernicus’s model did NOT fit the observational data very well

- Galileo made his telescope and found that Copernicus’ model was supported by

evidence

Tycho andd Kepler- Tycho Brache wanted to make accurate measurements of the planets motion

- Tchyo’s Data was successfully interpreted by the German mathematician scientist

Johannes Kepler in the early 1600s

- Kepler’s Laws

- 1st: determined that the orbits of the planets were not perfect circles, but ellipses,

with the sun at one focus

- 2nd: planets move faster when it is closer to the sun and slower when it is farther

away

- Why?

Gravity Gravity is an attractive force between any two objects that depends on the masses of

the objects and the distance between them.

Gravity applies to all objects that have a mass.

Gravity has an infinite range.

Law of Universal GravitationIsaac Newton- 1660 was studying the motion of the planets and their relationship to

one another.