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