Forces and Motion
the change in an object’s position with respect to time and in comparison to the position of other objects used as reference points
Motion
a push or pull that can change the motion of an object
Force
Newton’s first law of motion states that
a body at rest remains at rest and a body in motion continues to move at a constant velocity unless acted upon by an external force (law of inertia).
Newton’s second law of motion states that
acceleration is directly proportional to force and inversely proportional to mass (F = ma or a = F/m).
Newton’s third law of motion states that
for every action force, there is an equal and opposite reaction force.
A change in motion caused by an unbalanced force acting on an object; includes increasing speed, decreasing speed, or a change in direction
Acceleration
A student conducts an experiment in which he drops two balls off a table to determine the force of impact. The ball with the larger mass makes a bigger dent in the sand pit than the ball with the smaller mass.
This describes Newton’s __________ Law
Second
A train is resting on a track when another train with several more cars bumps it and causes it to move forward 10 meters. This is an example of
acceleration
A dog is chasing you at a speed of 10 m/s to the west. You are running away from him at a speed of 8 m/s to the west. This scenario describes _______________
velocity
A boulder sits at rest on top of a mountain. What conclusion can be made about the forces acting on the boulder?
forces are balanced
A baseball bat hits a baseball with a force of 100 Newtons. What is the force and its direction exerted by the ball on the bat?
100 N
system that uses coordinates or background objects to establish position or to measure movement of a point in space
Frame of Reference
A measure of how much matter is present in a substance
Mass
The sum of all the forces acting on an object
Net Force
A straight path that an object can move along
Direction
According to Newton’s Third Law, if someone jumps off a skateboard, the skateboard will roll backwards because–
for the force that sent the person forward, there is an equal force pushing back on the skateboard.
Objects that affect one another
Interacting Objects
A tool that measures a pulling force by the tension on a spring in units of newtons
Spring Scale
Unit of measurement for force
newton
To strike or hit something with any amount of force
Collide
The nozzle of a rocket is pointed downward so that as fuel is ignited, the exhaust pushes downward. Why is this arrangement necessary for a rocket to function properly?
As fuel is combusted, the rocket pushes the gases backward and the gases push the rocket forward.
Which of the scenarios described in the table show equal and opposite reaction forces?
A rocket launched into space
A train moving at a constant speed
A girl circling on a carousel
A rocket launched into space
Students are investigating how mass affects the force needed to move an object. They attached a wooden block to a spring scale and placed a 10 g mass on top of the block and pulled it 50 cm across the table.
Which of the following changes to their setup would result in a larger force reading on the spring scale?
Using a 20 g mass
Students are using an air rocket to investigate the relationship between force and an object’s motion. Students pump air into the rocket, then release the rocket, and the compressed air pushes the rocket upward. In order to vary the amount of force acting on the rocket, which of the following should the students change in each trial?
The amount of air pumped into the rocket
The head of a hammer is often made of steel. This makes the head heavy, which helps create a strong force for driving nails. Steel is also strong. The head of a hammer must be strong to resist what force?
The force of the nail pushing in the opposite direction