Motion & Forces Learning Target Study Guide
1. I can create and test a model depicting motion.
Since this target is creating a model and testing it, it is assessed in class labs and activities.
 We can use vectors to show motion of objects. Vectors are arrows of varying lengths/
sizes that can show the force or motion of an object.
 We can use graphs to show the motion of an object. Distance-Time graphs show the
velocity of an object as well as if the object is moving toward or away from it’s point of
origin and the position of the object at various points in time. Velocity-time graphs
show objects acceleration- the rate at which an object is speeding up or slowing down.
 We can use pictures of objects to show the motion of an object.
 We can use formulas to show speed, velocity, acceleration.
2. I can explain the motion of an object from a real-life situation.
In order to determine if an object is moving, you must relate it to a reference point. If you are
traveling in a car going down the interstate at 70 mph, you could be sitting still, sleeping, or
reading. In relation to the car and the other items in the car, you are not moving. In relation to
other cars going along the road, you are moving.
An objects motion is explained in terms of
 Speed- its distance divided by its time. Units are generally meters per second (m/s).
This can be determined from a graph by looking at the total distance an object went
divided by the total time it took to get there.
 Velocity= speed + direction
 Acceleration= The rate that something is speeding up or slowing down. (You could be
speeding up slowly or speeding up quickly- you could ease on the brakes or slam on the
brakes in a car). You find acceleration by taking the objects final velocity – its initial
velocity divided by the change in time it took to go from one velocity to another (vfvi/Δt). Units are usually meters per second squared (m/s2). Negative acceleration is the
same thing as deceleration and means the object is slowing down as opposed to
speeding up.
3. I can determine the net force of an object.
The net force of an object is the sum of all the forces acting on it.
 If two forces are pushing or pulling in the SAME direction, you would add the forces
together. An example would be if two people were pushing a car that had run out of
gas. They are both pushing the car in the same direction, so you would add the force
that each one is pushing with and the car would move in the direction of their force.
 If two forces are pushing/ pulling in OPPOSITE directions, you would subtract their
forces from each other, and the motion would be in the direction of the larger force.
For example, if two teams were playing tug-o-war and the teams were pulling with
different amounts of force. You would subtract the total force each team was pulling
with and the rope would be pulled in the direction of the larger force (strongest team).
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4. I can describe Newton’s 1st Law and give a real-life example.
 Newton’s 1st Law of Motion is often called the Law of Inertia and states that an object at
rest will remain at rest and an object in motion will remain in motion traveling at a
constant speed in a straight line forever until an unbalanced force acts on it.
 Inertia is a property of matter that resists any change in motion and depends on mass.
The more mass an object has, the more inertia it has; the less mass, the less inertia.
Examples:
 This is the reason we wear seatbelts! When a car is stopped at a stop light (at rest) and
you take off quickly, the passengers are pushed back into their seats (want to stay at
rest). After the car is moving and brakes suddenly, the passengers all continue to move
forward (want to stay in motion.)
 Pulling a cloth from under the dishes- If you pull a tablecloth quickly (must overcome
friction), the dishes should stay on the table because they want to stay at rest.
 An empty shopping cart is easy to get going, change directions, and stop because it has
little inertia (small mass). A full shopping cart has more mass, so it is harder to get
moving, difficult to turn around corners (wants to go in a straight line), and more
difficult to stop. Likewise with small and large vehicles and stopping distance.
5. I can describe Newton’s 2nd Law and give a real-life example.
 Newton’s 2nd Law of Motion is often called the Law of Acceleration. It states that the
force an object has is equal to the object mass and its acceleration. (mathematically
written F=ma)
Examples:
 A slow moving bullet has little force because it has small acceleration while a speeding
bullet has a lot of force because it has large acceleration (mass stays the same). Slow
moving train has a lot of force because of its large mass.
6. I can describe Newton’s 3rd Law and give a real-life example.
 Newton’s 3rd Law of motion is often called Action-Reaction or Equal and Opposite. It
states that for every action force, there is an equal and opposite reaction force.
Examples:
 A swimmer can swim because of Newton’s 3rd Law. The action force is the swimmers
hand pushing down on the water. The reaction force is the water pushing up on the
swimmers hands. The forces are equal in magnitude and opposite in direction, allowing
the swimmer to stay above water and move in the direction they wish.
 When paddling a boat, you push the oars backward with a certain amount of force in
order to move the boat forward with the same amount of force.
 A rocket moves upward with an equal force of the fuel pushes down from the end of the
rocket.
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7. I can predict and test motion using the conservation of mechanical energy and conservation of
momentum.
 The Conservation of Mechanical Energy states that the total amount of mechanical
energy in a system (potential energy + kinetic energy) remains constant. In motion, if
something stops moving (motion energy), that motion energy had to be transformed
into another form of energy. In the case of a pendulum swinging. The pendulum at its
highest point has all potential energy. As it falls to it’s lowest point, that kinetic energy
is transformed to motion energy, then back to potential energy as it goes up again.
Eventually the pendulum will stop moving because some energy has been converted to
heat from friction between the pendulum and the air. Regardless, the energy can be
accounted for, so the total amount of energy has not changed, only changed forms.
 Momentum of an object is its mass times its velocity (p=mv). The more massive an
object is or the faster it is moving, the more momentum it has. The less massive or if it
is moving slowly, the less momentum it has. For example, a baseball that is simply
tossed to you has little momentum compared to a baseball thrown at a very high speed.
A bowling ball simply tossed to you would have more momentum because it is more
massive than the baseball. Something that is not moving has NO momentum.
 The Conservation of Momentum says that the momentum in a system (particular
situation) does not change. This goes with Newton’s 3rd law of motion. If a rocket has
fuel pushing down out of its rocket boosters, it is going to push the rocket up with equal
force in the opposite direction. The momentum of the rocket going upward will equal
the momentum of the fuel going downward.
8. I can describe motion due to gravitational acceleration.
 When the Earth’s gravity is the only thing force acting on an object, the object is said to
be in free fall. Free fall acceleration is the accelerating toward the center of Earth. With
no air resistance, all objects falling near Earth’s surface will accelerate at the same rate,
regardless of their mass. In other words, The Earth loves all objects the same, so all
objects fall toward earth at the same rate. The rate of gravitational acceleration is 9.8
m/s2. This means that for each second an object is falling toward earth, it is moving 9.8
m/s faster than the second before.
 Since all objects fall at the same rate, the mass of the object does not matter. A golf ball
and a bowling ball dropped from a tall building at the same time will hit at the exact
same time. The only thing that gets in the way is an objects air resistance. On Earth, a
feather and a hammer would fall at different rates due to air resistance. On the moon
where there is little to no air resistance, a feather and a hammer would land at the same
time (it has been done).
 An object can reach a maximum velocity, called terminal velocity, and stop accelerating
when the air resistance of an object becomes equal to its weight. For example, when a
skydiver is falling toward earth with their parachute closed, they are accelerating toward
earth at 9.8 m/s2 due to gravity. As they fall, the air is pushing up on them. When the
air resistance and the force of gravity become equal, they reach terminal velocity. After
they open their parachute, they increase their air resistance, slowing their velocity, and
changing their terminal velocity.
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