State Newton's 1st Law .

Objects maintain their states of motion (rest; constant velocity) unles acted upon by a net external (outside) force

What is inertia?

An objects resistance to changes in motion.

How can you get a moving object to change direction?

Apply an external force.

If an object has more mass, it has more _________.

Inertia.

Give an example of Newton's First Law.

ex) object at rest; object with constant velocity; etc.

State Newton's Second Law. (formula is acceptable answer)

F = ma

Force is the product of mass and acceleration. 

A small plane has a mass of 2000 kg and accelerates at 15 m/s² down the runway.  What is the magnitude of the force acting on the plane?

30,000 N

If a non-zero net force is acting on an object, what is happening to the object?

It is accelerating (changing velocity).

A 5.0 kg block is on a frictionless horizontal surface.  F1 = 7.0 N and pulls to the left.  F2 = 15.0 N and pulls to the right.  What is the acceleration (magnitude and direction) of the block?

8N, to the right.

A wagon is pulled with a constant force by a child. While it is being pulled, another small child is continuously pouring sand into the wagon. How is the acceleration of the wagon affected? Explain.

Acceleration decreases. F = ma. If Force remains constant and mass increases, then acceleration must decrease. m and a are inverse.

State Newton's Third Law.

Forces come in pairs; when one object exerts a force on another object, the second object also exerts an equal (magnitude) and opposite (direction) force on the 1st object.

Give an example of Newton's Third Law.

ex. normal force, etc

Cart 1 has a mass of 2 kg.  Cart 2 has a mass of 4 kg.  They are pushed apart by a spring.  The spring exerts 5 N of force onto cart 1. How much force is exerted onto cart 2?

5N; Spring pushes cart 1 with 5N, cart 1 pushes back with 5N, spring therefore will push 5N on car 2 as well.

Driving along one day, a giant beetle splatters against my windshield. Which is greater, the force acting on the windshield or the force acting on the beetle?

Trick! Both the same!

True or False: In order to make a wagon move forward, a horse must pull harder on the wagon than the wagon pulls on the horse.

FALSE!

The horse pushes on the ground and in turn the ground pushes on the horse propelling it forward.

Draw a free body diagram for a ball falling (ignore air friction).

Draw a free body for a book sitting on a table.

Draw a free body diagram for an object falling at terminal velocity.

Draw a free body diagram for a car accelerating to the right (include friction).

Draw a free body diagram for a car that is moving at a constant velocity (include friction).

What type of friction must be overcome in order to start an object moving?

Static Friction.

Define Kinetic friction.

The friction that occurs when objects slide against each other.

A mass of exactly 40 kg is sitting on a flat wooden board.  A spring scale is attached to the mass.  A reading of 250 N is needed to just start to drag the mass over the board. 

a) 250 N

b) 400N

c) 0.6

Give 2 factors that affect the coefficient of friction.

ex) roughness of surface, temperature, dry/wet, grease/lubricant.

A force of 50 N is required to start a 10 kg box moving across a horizontal floor. What is the coefficient of static friction between the box and the floor.

0.5

Force of friction is equal to force applied because the box just started to move. Normal force is the mass (10 kg) multiplied by acceleration due to gravity (9.8 m/s2). Coefficient of friction is Force of friction divided by the normal force (50 N/100 N).

Surface Area