Motion and Forces Notes

Speed

• To describe how ______something is traveling, you have to know two things about its motion.

• One is the ______it has traveled, or how far it has gone.

• The other is how much ______it took to travel that distance.

Average Speed

• To calculate average speed, divide the ______traveled by the ______it takes to travel that distance.

• ______

Average speed (in m/s) = distance traveled (in m) divided by time (in s) it took to travel the distance

s = d

• Because ______is calculated by dividing distance by time, its units will always be a distance unit divided by a time unit.

• For example, the average speed of a bicycle is usually given in ______.

• Average speed is useful if you don't care about the details of the ______.

• When your motion is speeding up and slowing down, it might be useful to know how fast you are going at a ______time.

Instantaneous Speed

• The instantaneous speed is the speed of an object at any ______of time.

Constant Speed

• Sometimes an object is moving such that its instantaneous speed doesn’t ______.

• When the instantaneous speed doesn't change, an object is moving with ______.

• The average speed and the instantaneous speed are the ______.

Calculating Distance

• If an object is moving with constant speed, then the distance it travels over any period of time can be calculated using the equation for ______.

• When both sides of this equation are multiplied by the time, you have the equation for ______.

• Notice that the units of time in the speed, s, and in the time, t, have to be the same.

• Otherwise, these units of time won't ______.

• Distance Equation

Distance traveled (in m) = average speed (in m/s) X the time (in s)

d = ______

Velocity

 The velocity of an object is the ______of the object and its ______of motion.

 Velocity changes when the ______changes, the ______of motion changes, or ______change.

 If you are walking north at a constant speed then turn east, continuing at the same speed, you have changed your ______.

Acceleration

 Acceleration is the change in ______divided by the time needed for the change to occur.

 If the speed but not direction of an object is changing, the object is ______.

 The ______of the acceleration depends on whether the object is speeding up or slowing down.

 A marble rolling in a straight line down a hill ______.

Its motion and acceleration are in the ______direction.

 A marble rolling in a straight line on a level surface with ______.

Its acceleration is ______.

 A marble rolling in a straight line up a hill ______.

Its motion and acceleration are in ______directions.

Calculating Acceleration

 If an object changes ______but not ______then its acceleration can be calculated from the following formula.

 Acceleration Equation

Acceleration (in m/s2) = final speed (in m/s) – ______(in m/s) divided by time (in s)

a = (sf – si)

Graphing Speed

 The acceleration of an object can be shown on a ______.

 The line on the graph ______when acceleration is in the direction of motion.

 A horizontal line shows that the acceleration is ______.

 Anytime you slow down, acceleration is ______the direction of motion, and the line on a speed-time graph will slant ______.

Force

 A ______is a push or a pull.

 In SI units, force is measured in ______(N).

 One newton is about the amount of force it takes to lift a quarter-pound hamburger.

Force and Acceleration

 For an object's motion to change, a force must be ______to the object.

 This force causes the object to ______.

 A force also can change the ______of an object's motion.

 An object has acceleration when its ______of motion changes.

 Anytime an object's speed, or direction of motion, or both change, a ______must have acted on the object.

Balanced and Unbalanced Forces

 More than one ______can act on an object without causing its motion to change.

 Two or more forces are ______forces if their effects ______each other and they do not cause a change in an object's ______.

 If the effects of the forces don't cancel each other, the forces are ______forces.

Combining Forces

 When more than one force acts on an object, the forces ______.

 The combination of all the force acting on an object is the ______.

Newton’s Laws of Motion

 ______realized that he could explain the motion of objects using a set of principles, which in time came to be called Newton's laws of motion.

Newton’s First Law

Friction

Newton's ______law of motion states that an object will not change its motion unless an ______force acts on it.
Therefore, an object that is not moving, like a book sitting on a table, remains at rest until something pushes or pulls it.
A moving object, like a ball moves in a straight line with ______unless an unbalanced force acts on it.
After the ball has been hit, it will move along the ground in a straight line until it is acted on by another ______.
A book slides across a table, slows down, and comes to a stop.
Because its motion changes, a ______must be acting on it and causing it to stop.
This force is called ______.
Friction is a force between two surfaces in contact that ______the motion of the surfaces past each other.
To keep an object moving when friction is acting on it, you have to keep pushing or pulling on the object to overcome the ______.
In general, the ______the surfaces are, the greater the friction will be.

Inertia and Mass

The tendency to ______a change in motion is called ______.
The more matter an object has, the ______it will be to move or stop.
______measures the quantity of matter.
The more mass an object has, the ______its inertia is.

Newton’s Second Law

 Newton's ______law of motion states that if an object is acted upon by a net force, the ______of the object will be in the direction of the net force, and the acceleration equals the net force divided by the mass.

 Newton’s Second Law Equation

acceleration (in m/s2) = ______(in N) divided by mass (in kg)

a = Fnet

 The more ______an object has, the more ______it has, so the harder it is to accelerate.

When pushing a refrigerator, which has a large mass, a large force is required to achieve a ______acceleration.
If you were to push an empty grocery cart with the same force, its acceleration would be ______.

Newton’s Third Law

 According to Newton's third law, when one object exerts a force on a second object, the seconds object exerts an ______force in the ______direction on the first object.

 When you walk, you ______back on the sidewalk and the sidewalk pushes ______on you with an ______force.

 The force exerted by the first object is the ______force.

 The force exerted by the second object is the ______force.

 The action and reaction forces are equal, but in ______directions.

Force Pairs Act on Different Objects

 If forces always occur in ______but ______pairs, how can anything ever move? Won't the forces acting on an object always cancel each other?

 When you push on the book, your force is acting on the book.

 When the book pushes back on you, its force is acting on ______.

 Because the forces act on ______objects, they don't ______.