Physics Unit 1: Forces

A tow truck exerts a force of 3000 N on a car, which then accelerates at 2 m/s2. What is the mass of the car?

1500kg

Is friction a long range or a contact force?

A contact force

An object is moving to the right with a constant speed. What can be concluded about the forces acting upon the object?

All the individual forces acting upon the object are balanced.

True or false: A mathematical model is physical, like a miniature version of something to scale.

False

True or false: A object moving at a constant speed should always have 0 forces acting on it.

False

True or false: If a person throws a football, the force of the person on the football should always be included in the force list.

False

True or false: Magnetism is an example of a contact force.

False

True or false: On your picture of the situation, the circle should include everything solid, but not gases or liquids.

False

True or false: Pushes and pulls should be shown with different types of arrows. For example, a push should be shown as an arrow going toward the center.

False

True or false: When drawing someone standing on the ground, you should include the force of the Earth on the person only.

False

True or false: When writing mathematical models, your slope should always be unitless.

False

True or false: When you list the y and x variables, it doesn't really matter which is which.

False

True or false: You only need to include contact forces on force diagrams.

False

The first scientist to introduce the concept of inertia was

Galileo

Which of the following statements about inertia is true?

Inertia is the natural tendency of a stationary object to resist motion.

Which of the following can be explained using Newton's first law of motion?

It explains why a stationary object remains stationary.

All except one of the following require the application of a net force. Which one is the exception?

Maintaining an object in motion at a constant velocity

Which force allows you to pick up a cup?

Static friction

What is ALWAYS true of an object that is acted upon by an unbalanced force?

The object is accelerating

Which one of the following is known for certain to be true of an object that is at rest?

The object is experiencing a balance of forces

True or false: A formula is an example of a mathematical model.

True

True or false: A stopped object counts as traveling at a constant speed.

True

True or false: Before drawing arrows (vectors), you should list all the forces on an object.

True

True or false: The force diagram only represents a moment in time. 1 second later, the diagram might look different.

True

True or false: The slope of the line of best fit means the rate of change for the y-variable as you change the x-variable.

True

True or false: You should write separate summation equations for the x and y dimension.

True

A certain force causes a 50 kg person to accelerate at 1.0 m/s2. The same force applied to a 75-kg person would cause

a smaller acceleration

A package falls off a truck that is moving at 30 m/s. Neglecting air resistance, the horizontal speed of the package just before it hits the ground is

about 30m/s

If an apple experiences a constant net force, it will have a constant

acceleration

An object is moving to the left with a constant speed. What can be concluded about the forces acting upon the object?

all the individual forces acting upon the object are balanced

Newton's first law of motion applies to

both objects that are at rest and those that move at constant velocity.

Blunders

careless mistakes, such as copying down wrong number, forgetting a digit, misread a scale, etc

If no external forces act on a moving object, it will

continue moving at the same speed

Systematic errors

due to identified causes, can in principle be eliminated, result in measurements consistently too high or too low, 4 kinds 1) instrumental: thermometer always reads 2 degrees higher than reality 2)observational: reading wrong number b/c you look at wrong angle 3) environmental: electrical power "brownout" 4) theoretical: due to simplification of model system or approximations in equation

If less horizontal force is applied to a sliding object than is needed to maintain a constant velocity, the object

eventually slides to a stop

A moving van with a stone lightly glued to the midpoint of its ceiling smoothly moves at constant velocity. When the glue gives way, the stone falls and hits the floor

exactly below the midpoint of the ceiling

When compared to a less massive object, a more massive object will always

have a greater tendency to resist changes in its state of motion

Sliding friction will generate

heat and sound

An object with twice as much mass as another object has twice as much

inertia

What property of an object describes its natural tendency to resist an acceleration?

inertia

When you flick a card from beneath a coin that hardly moves, you're illustrating

inertia

Which concept is being illustrated when a tablecloth is quickly yanked beneath dishes resting on a table?

inertia

If the net force on a cart is tripled, the cart's acceleration

is three times as much

Whenever the net force on an object is zero, its acceleration

is zero

Galileo taught us that if you roll a ball along a level surface it will

keep rolling if friction is absent

A wheel on a car turns clockwise. A person applies the brakes until the car stops. The type of friction between the brakes and the pads is

kinetic friction

A hockey puck is set in motion across a frozen pond. If ice friction and air resistance are neglected, the force required to keep the puck sliding at constant velocity is

none (???? check)

If the forces acting upon an object are balanced, then one can be certain that the object is _____.

not accelerating

A hockey puck sliding across the ice finally comes to rest because

of friction

A car by itself is capable of a certain maximum acceleration. When it tows a car of the same mass, its maximum acceleration is

one half

Random errors

positive and negative fluctuations that cause about one-half of the measurements to be too high and one-half to be too low 1) observational: ie errors in judgment of an observer when reading the scale of a measuring device to the smallest division 2) environmental: unpredictable fluctuations in line voltage, temperature, or mechanical vibrations of equipment

Inertia is defined as a

property of matter

Galileo's interpretation of motion differed from Aristotle's in that Galileo emphasized

rates of time

Galileo's use of inclined planes allowed him to effectively

slow down the ball's changes in speed.

If you double the net force on an object, you'll double its

speed

When no forces act on moving objects their paths are normally

straight lines

When a net horizontal force of 250 N acts on a 50-kg cart that is free to roll on a level surface,

the cart accelerates at 5 m/s2.

A force of 1 N accelerates 1-kg box at the rate of 1 m/s2. The acceleration of a 2-kg box by a net force of 2 N is

the same

Friction happens because of

tiny bumps moving over each other AND stickiness between molecules