Unit 3 - Forces and Newton's Laws

12/17

Force

Any push or pull on an object.

Elementary Forces

• Strong

• Weak

• Electronegative

• Gravity

Contact forces

• Spring

• Air resistance (drag)

• Tension

• Friction

• Applied

• Normal

Mass

The amount of matter in an object.

• Measured in grams and kilograms

Weight

The force of gravity on an object.

• Measured in Newtons.

g - Strength of Gravity

How fast an object accelerates on a planet.

• determined by the planet & affects the force of gravity (weight).

Friction

A force that opposes motion.

Air friction

Occurs when an object passes through air.

Rolling friction

Occurs when 1 object is rolling against another.

Sliding friction

Occurs when 2 objects slide against each other.

Static friction

Occurs between a stationary object and a surface, preventing the object from moving.

Balanced forces/Equilibrium

When all forces cancel each other out.

• Net force = 0 N

Unbalanced forces

When there is a net force and not all forces are cancelled out.

• Have an acceleration.

Free-body diagram

Diagrams that are used to show the size and direction of all forces acting upon an object in a given situation (system).

Net force

The total forces acting on an object.

Forces to the right or up are...

postive

Forces to the left or down are...

negative

Forces going in the same direction are...

added

Forces going in opposite directions are...

subtracted, and you keep the direction of the larger one.

Newton's first law

Known as the law of intertia

Inertia

The resistance to the change in motion.

• More mass = more inertia.

What are the names of the two forces that come in pairs?

Action and reaction

Are action and reaction forces in the same or opposite direction?

Opposite

The equal and opposite forces don't have a net force of 0 because...

The forces are acting on different things, rather than just one object.

Newton's second law

a = F/m

Newton's third law

Forces come in pairs that are the same size, but in opposite directions.

Action force

The force exerted by one object onto another.

Reaction force

The equal and opposite force exerted back on the first object by the second.

Momentum

How hard it is to stop an object.

• Relationship between mass and speed.

Law of conservation of momentum

In a collision, the total momentum of a system before a collision always equals the total momentum after the collision.

Elastic Collision

The object bounce off of each other.

Explosion Collision

The objects stick together (hit and stick)

Hit and Stick Collision

The objects start together and then separate.

Which law is associated with inertia?

Newton's first law

If you increase the force on an object, the acceleration...

increases

If you use the same force on a less massive object, the acceleration is...

greater

Which law states that force is dependent on the mass and acceleration of an object?

Newton's second law

What causes an object to slow down or speed up?

A change in force or mass

Which law is known as the law of action-reaction?

Newton's third law

Which law explains why when you bump into something you fall backwards?

Newton's third law

If you double the force of an object, the acceleration...

doubles

If you double the mass of an object, the acceleration...

cuts in half.

1N = _______

kg * m/s²

What two things can the presence of an unbalanced force change?

Speed and direction

Why is a full shopping cart harder to turn than an empty shopping cart?

The full shopping cart has more inertia .

A ball is kicked and it starts rolling down a level sidewalk. As it rolls, it slows down and stops. Why?

Frictional force acts on the ball to stop it.

A flyswatter swats a fly. When the two interact how do the action-reaction forces compare?

The forces were equal.

An object's inertia is solely dependent on the object's ________.

mass

When Kris drives to work, he always places his bag on the passenger's seat. By the time he gets to work, his bag has fallen on the floor in front of the car. Why does this happen?

When the car stops, the bag stays in motion, and so it keeps moving forward.

A rocket can fly into space because:

The rocket pushes exhaust gases backward, and there is an equal and opposite reaction pushing the rocket forward.

Two skaters push off of each other on a frictionless surface. The person in blue has a mass of 90 kg and the person in orange has a mass of 45 kg. How will their speeds after they push off each other compare?

The orange person will have twice the speed of the blue person.

A 0.16 kg cue ball is travelling at has a velocity of 11.3 m/s and has a momentum of 1.8 kg*m/s. It strikes 3 balls, each with a mass of 0.16 kg. What is the total momentum of all the balls after the strike?

1.8 Kg*m/s