Forces Topic Lessons

Forces

Forces: Objectives

- I can describe a force.

- I know the unit of measurement for force.

- I know the difference between mass and weight.

​FORCES

Balanced Forces

A good example of balanced and unbalanced forces is a
tug-of-war between two teams of students. If the opposing
teams are of equal strength, neither team can move the
other, because their net force is zero and the forces are
balanced. This is shown in the diagram to the right.

The same result occurs when a force pushes on an
unmovable object, or when friction prevents the motion of an
object because not enough force was applied to overcome
that friction. In both of these cases, the two forces are equal
but in opposite directions—they cancel each other out.

Balanced Forces

Balanced forces exist when all of the forces acting
on an object cancel each other out, resulting in a
net force of zero. If the object pulled down by
gravity is resting on the ground, which is strong
enough to push up with equal force, the two
forces cancel each other out, and no motion
results In the diagram to the right, the down arrow
(gravity) and the up arrow (ground support) are of
equal length but opposite direction. If the net force
is zero, the forces are balanced, and no
acceleration (change of motion) occurs.

Unbalanced Forces

Unbalanced forces exist on an object when the net
force acting on that object is greater than zero. In the
above example, gravity pulls down more strongly than
the air resistance pushes back. The two forces can be
represented by arrows, as shown to the right. The size
of the arrows represent the relative strength of the two
forces. The larger down arrow represents gravity, and
the smaller up arrow represents air resistance. By
subtracting the down arrow length from the up arrow
length, the net force arrow shows the smaller
downward acting force

Unbalanced Forces

The same result occurs when a force pushes on an
unmovable object, or when friction prevents the motion
of an object because not enough force was applied to
overcome that friction. In both of these cases, the two
forces are equal but in opposite directions—they cancel
each other out.

If Team B becomes tired, and pulls less hard than Team
A, Team B eventually lose because they were moved
(accelerated) to the left, the direction of the greater
force.

Multiple Choice

What is the net force on this box?

• 30 N left

• 25 N right

• 5 N left

• 55 N right

Multiple Choice

_________ opposes motion. (___________tries to stop motion from happening)

• Acceleration

• Gravity

• Friction

• Velocity

Multiple Choice

What force holds the planets in motion around the sun?

• Magnetic

• Electrical

• Gravitational

• Air Resistance

Multiple Choice

The illustration below shows what happened when a balloon touched a girl’s hair.

Which type of force do you think caused the girl’s hair to cling to the balloon?

• magnetic force

• frictional force

• electrical force

• gravitational force

Multiple Choice

Magnets can be a useful tool. Look closely at the picture below which shows a magnet and various metal objects.

What do you think will happen as the magnet moves closer to the metal objects?

• The magnet will attract the objects.

• The magnet will become heavier.

• The magnet will push the objects away

• Nothing will happen to the objects

Multiple Choice

Which force acts as an upward push in a fluid?

• Thrust

• Buoyancy

• Friction

• Elastic Force

Multiple Choice

______ between your feet and a sidewalk prevents you from slipping as you walk.

• Gravity

• Friction

• Weight

• Inertia

Multiple Choice

Which force is caused by STRETCHING?

• Thrust

• Elastic Force

• Bouyancy

• Friction

Multiple Choice

A measure of how much MATTER is in an object

• Mass

• Velocity

• Weight

• Net Force

Multiple Choice

Forces that do NOT need to touch. Act at a DISTANCE

Fuerzas que NO necesitan tocar. Actuar a DISTANCIA

• Contact forces

• Non Contact forces

Multiple Choice

Some forces can act over a distance, and others can only act by contact. Which type of force can act only when two objects touch each other?

• gravitational

• frictional

• electrical

Floating and Sinking

Some things float and some things sink. Upthrust pushes objects against the other forces acting on the object if it is in a liquid or gas. The result is called floating.

Multiple Choice

• Balanced

• Unbalanced

Multiple Choice

• Balanced

• Unbalanced

Open Ended

Is this Balanced or Unbalanced?

What is the Net Force?

What is the Direction of the Force?

Open Ended

Is this Balanced or Unbalanced?

What is the Net Force?

What is the Direction of the Force?

Open Ended

Is this Balanced or Unbalanced?

What is the Net Force?

What is the Direction of the Force?

Multiple Choice

Which of the following is an example of an unbalanced force?

Multiple Choice

A contact force is from

• objects physically touching

• far apart objects

• not touching object

• always a pull

Multiple Choice

The three examples pictured are of

• Non-contact Forces

• Contact Forces

Multiple Choice

Normal force is a...

• Contact Force

• Non-Contact Force

Multiple Choice

What is a NON-CONTACT force?

• A push or pull force where the objects are not touching

• A push force where the objects are touching.

• An example would be pulling open a door.

• The only type of force that exists in the world.

Multiple Choice

What are the three NON-CONTACT forces we are studying this unit?

• Gravity, friction, air resistance

• Forces, motion, human body systems

• Friction, electricity, muscular system

• Gravity, electricity, and magnetism

Multiple Choice

Forces are only present when things are moving.

• True

• False

A Force is a push...

...or a pull

...or any action that has the ability to change motion.​

Open Ended

Can you think of a specific example of a type of force?

Force is an action! You need force to start things moving, and to make any change to an objects motion.

Forces can increase or decrease the speed of an object.

Forces can also change the direction in which an object is moving.

A force can start movement.

In this example, a force is being applied to a golf ball sitting still, to start movement.

A force can also stop a moving object.

In this example, a force is being applied to the moving ball to stop it.

A force also changes the direction of an object.

In this example, wind is affecting the direction the soccer ball is traveling in, causing it to spin and turn and change direction.

Newton - a unit that measures force.

The newton is defined by how much force can change the motion of an object.

Multiple Choice

Friction is a force.

• True

• False

There are 4 Universal Forces

1. Strong Nuclear Force

2. Electromagnetic Force

3. Weak Nuclear Force

4. Gravity

(listed from strongest to weakest)

The nucleus of an atom is made of protons, which all have a positive charge. But similar charges repel each other. Positive pushes away positive and negative pushes away negative.

So what stops the atoms from flying apart and every atom and molecule in your body exploding into smithereens'!?!?!

​1. Strong Nuclear Force

​

The strong nuclear force does. It’s basically the glue that holds nucleus together, but it only works over very, very small distances.

2. Electromagnetic Force

This is what light is made of. No, really. I promise. And it is one million million million million million million times stronger than gravity. Seriously. Don’t believe me? Tell that to your sunburn this summer. The energy from electromagnetic forces that gives you a sunburn (UV Rays) travels millions of miles just to burn you. That's a strong force.

2. Electromagnetic Force

You don’t feel the sun’s gravity pulling on you as it moves through the sky, but you definitely feel light blistering your skin.

​

This force comes in waves, and emits light (visible and invisible).

2. Electromagnetic Force

The electromagnetic force is also responsible for what holds electrons in an orbit around an atom as the negatively charged electron orbits around the positively charged nucleus.

3. Weak nuclear force

The weak force is a force that leads to some kinds of radioactivity, as seen by the neutrons and protons leaving the atom.

​

Radioactivity is when ​an atom is unstable and loses some of its energetic particles.

4. Gravity

The one we might think is the strongest, is actually the weakest. But the more stuff you have (the more mass) the stronger gravity becomes, and the Earth is made of a LOT of stuff, so the gravitational pull of the Earth feels very strong indeed.

4. Gravity

​

The universal force of attraction acting between all matter.

Earth's gravity creates a force called weight that pulls on everything around you.

Weight is a force that comes from gravity pulling down on any object with mass. The more the mass, the greater the gravity.

Open Ended

What do you think the difference between mass and weight is?

The difference between mass and weight is that weight is a force that involves gravity.​

​

MASS IS NOT A FORCE!

​

weight (W) = mass (m) X gravity (g)

This is why your weight on Mars is less than on Earth.

Even though your mass is the same on Earth and Mars, the gravitational pull on you is different.

​

Mars has less of a pull on you because it has less mass than Earth.​

Multiple Choice

This type of force is responsible for holding atoms together at their nucleus.

• Strong nuclear

• Weak nuclear force

• Gravity

• Electromagnetic

Multiple Choice

This type of force is responsible for planets orbiting.

• Strong nuclear

• Weak nuclear force

• Gravity

• Electromagnetic

Multiple Choice

This type of force is responsible for the light you see.

• Strong nuclear

• Weak nuclear force

• Gravity

• Electromagnetic

Multiple Select

This type of force is responsible for The Hulk's superpowers.

• Strong nuclear

• Weak nuclear force

• Gravity

• Electromagnetic

To sum up the 4 Universal Forces...

Strong Force

Gravitational Force

Weak Force

Electromagnetic Force

holds protons and neutrons together in the nucleus.​

force between all objects that contain with mass.

responsible for radioactivity.

holds electrons ​in orbit around an atom, travels in waves through space.