Force and Motion

Force and Motion

By John Toje

Force and Motion Review

Read through the slides and answer the questions as you go.

Multiple Choice

What is a Force?

• The distance

• Mass

• A push or pull

• Give me a failing grade

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

Multiple Choice

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

Which type of force 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 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

An object drops due to the force of _____________.

• inertia

• momentum

• friction

• gravity

Multiple Choice

What force holds the planets in motion around the sun?

• Magnetic

• Electrical

• Gravitational

• Air Resistance

Multiple Choice

This type of force resist motion between two surfaces that are pressed together

• contact
• gravity
• friction

Motion, Speed, Velocity, and Inertia Review

Motion is a change in position.

Speed is the distance an object travels in a certain amount of time.

Velocity is the speed and direction of a moving object.

Inertia is an object's tendency to resist a change in motion.

Forces

A force is a push or a pull on an object.

Force can be calculated with a formula:

force = mass x acceleration

(F=m x a)

Force is measured in units called Newtons (N).

Unbalanced Forces

Unbalanced Forces-When two forces acting on an object are not equal in size, we say that they are unbalanced forces.  Motion changes when we have unbalanced forces

Balanced Forces

When an object is at rest on a surface, such as the ground, its weight is balanced by the reaction force from the ground. The ground pushes up against the object. There is no acceleration with balanced forces.

Multiple Choice

Balanced or unbalanced?

• balanced

• unbalanced

Multiple Choice

What happens when two forces act in the same direction?

• the forces add together

• the forces cancel each other out

• the stronger force takes over

Friction

Friction is a force opposing the motion between two surfaces. For example: Tires on roadway.

Types of Friction

Sliding Friction is friction that occurs when one solid surface slides over another.

Static Friction is friction that acts on objects that are not moving.

Fluid Friction is friction on a solid object as it moves through a liquid or a gas.

Rolling Friction is when a wheel, ball, or cylinder rolls freely over a surface, as in ball and roller bearings

Multiple Choice

Which type of friction is pictured?

• rolling

• sliding

• fluid

Other Forces

Did you know that gravity is a force? When the only force acting on an object is gravity, the object is in a state called "free fall"

Another force to note is air resistance. Air resistance is a force that opposes the motion of objects that move through the air.

Multiple Choice

What is Newton's First Law known as? The Law of

• Friction

• Mass

• Inertia

• Gravity

Multiple Choice

What is Newton's First Law

• F=ma

• Every action has an equal and opposite reaction

• An object at rest stays at rest, an object in motion stays in motion. 

• Friction 

Multiple Choice

What is the net force?

• 20 N 

• 0 N 

• 400 N 

• 40 N 

Mass and Inertia

Newton's 2nd law states that The greater the mass of an object, the more force it will take to accelerate the object. 

This also ties in to inertia, an object's tendency to resist a change in motion. The greater the mass an object has, the greater inertia it will have.

Multiple Choice

The greater the mass an object has, the greater the inertia.

• True

• False

Multiple Choice

An object's velocity can be changed by changing its speed, its direction, or both.

• True

• False

Multiple Choice

Newton's second law of motion describes acceleration as force divided by __________.

• mass

• inertia

• speed

• direction

Multiple Choice

According to __________, the acceleration of an object is equal to the net force acting on the object divided by the object's mass. 

• Newton's Second Law

• Newton's Third Law

• Newton's First Law

Multiple Choice

F= mass * acceleration

A 20 kg bike accelerates at 10 m/s². what is the force acting upon it?

• 25 Newtons

• 20 Newtons

• 200 Newtons

• 10 Newtons

Newton's Laws of Motion

1st Law: An object at rest will remain at rest, and an object in motion will remain in motion unless acted on by an outside force.

2nd Law: An object accelerates because a force acts on it. The larger the force, the greater the acceleration. The larger the mass, the greater force needed to accelerate it.

3rd Law: For every action force, there is an equal and opposite reaction force.

Multiple Choice

A baseball player hits a ball with 400 N of force. How much force does the ball exert on the bat?

• 300

• 400

• 500

• Not enough info to tell

Multiple Choice

Your friend pushes you for making fun of him/her. What is the reaction force?

• You pushing back on your friend

• You pushing on the ground

• There is no reaction force

• Your friend pushing on the ground

Multiple Choice

When you jump up, you push the earth downwards. Why can't you tell that the earth has moved?

• The force of you jumping up doesn't actually push the earth down.

• The earth has much more mass so it doesn't move at all

• The earth is firmly rooted

• The earth has much more mass so you can't tell that it moved

Multiple Choice

In space, rockets move by shooting air backwards. What moves faster the air or the ship?

• Neither, they both move at the same speed

• The ship because it has more mass

• The air because it has less mass

• The ship because it is moving forwards

Multiple Choice

When you hit a tennis ball with a racket...

• The ball exerts more force on the racket

• The ball and racket exert the same force on each other

• The racket exerts more force on the ball

• It depends on how hard you hit it

Multiple Choice

Air resistance is considered to be a type of:

• motion

• speed

• friction

• weight

Multiple Choice

Which of the following would cause an increase in friction on our Hot Wheels ramp?

• add cooking oil to the ramp

• add sandpaper to the ramp

Multiple Choice

Which of the following is an example of Newton's 1st Law of Motion?

• When you swim, you push the water backward and the water pushes you forward.

• A soccer player races to the motionless soccer ball and kicks it to overcome inertia.

Multiple Choice

Which of the following is an example of Newton's 2nd Law of motion?

• A snowboarder turns sideways and digs the board into the snow. The snow stops the board.

• It takes more force to kick a soccer ball 5 meters than it does to kick a beach ball 5 meters.

Multiple Choice

Which of the following applies to Newton's 3rd Law of motion?

• Water shooting out of a water hose causes the hose to fly backwards.

• We wear seatbelts in the car in case the car stops suddenly.