Force, & Newton’s Laws of Motion

Force, Friction and Inertia

Force is a push or pull, can cause objects to speed up, slow down, or change direction. Unbalanced forces cause a change in motion, while balanced forces allow an object to keep doing what it is doing.

Friction is caused by two objects coming into contact with each otherand acts as an unbalanced force on an object

Inertia is the tendency of an object to resist motion, or to keep on doing what it is doing

Potential and Kinetic Energy

Potential energy An object at rest has

potential energy. EX: A rock sitting on a

cliff.

Kinetic Energy An object in motion

has kinetic energy. EX. A rock falling off

the cliff, when it is in the air, this is where it has kinetic energy.

Newton’s Law of Inertia

“An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon an outside force.”

Newton’s Law of Force and Acceleration

For example…

Newton’s Law of Action-Reaction

"For every action, there is an equal and opposite reaction."

Reaction

Action

Balancing Act

Law of inertia: The forces in the system are balanced so the object resists movement.

Law of force and acceleration: Since there is no net force, the acceleration is 0.

Law of action-reaction: The downward force of gravity is opposed by the upward force of the finger.

Static Can Race

Law of Inertia: Once the can began rolling it stayed in motion, until friction acted upon it.

Law of force and acceleration: Since the can is empty, the static force needed to move the can was small.

Law of action-reaction: As the can was being pulled by the static force of the balloon, the motion is opposed by friction between the can and the floor.

Gyrocopter

Law of Inertia: Once the gyrocopter began to fall, it continued falling until acted upon by the floor.

Law of force and acceleration: As the mass of the gyrocopter increased, so did force its force.

Law of action-reaction: As gravity pulls the gyrocopter down, air resistance is pushing up on the blades of the gyrocopter causing it to fall more slowly. When the mass increased, the downward force of gravity increased, causing the gyrocopter to fall faster.

Speed, Acceleration, Velocity, & Work

S = distance(m)/time(s, or h), labeled mps or mph

A= force(N)/mass(kg) or A= Change in velocity/time, labeled m/s squared

V=distance(m)/time(s), labeled in m/s

W(joules, J)=force(N) * distance( in meters),

Weight = mass (g) x acceleration due to gravity (9.8 m/s squared)

1. Which of the following equations correctly describes the amount of work done?

A. Force x EnergyB. Force x DistanceC. Speed x TimeD. Speed x Force

2. If a boy pushes a box that weighs 20kg with 30N of force 7 meters, how much

work has he done?

A. 211 JB. 210 JC.210 ND.110 J

3. What is the acceleration of an object that weighs 22kg and is pushed with a force of

132 N?

A. 1 NB.4.5 m/sC.6 m/s squaredD.8 m/s squared

4. If a 100kg object was pushed with the force of 75N for 5 meters, what is the

work in joules?

A. 375 NB. 375 JC. 355 JD. 377 N

5. If 20N of force lifted 2 kg 1.5 meters high, what is the work in

joules?

A. 40 JB. 30 NC. 35 JD. 30 J

6. What two variables does the acceleration of an object depend on?

A. Force and AccelerationB. Force and GravityC. Force and MassD. Force and Velocity

7. What is needed for an object to overcome the force of friction?

A. a balanced forceB. frictionC. an unbalanced forceD. air resistance

8. You are racing a cart down the hallway. If you go 10 meters in 5

seconds, what is your speed?A. 2 meters per secondB. 2 miles per hourC. 50 meters per secondD. 2 meters per hour

9.What is the net force of a 240kg object moving at 60 m/s squared?

A. 14444 NB. 14400 m/sC. 14400 ND. 14340 N

10. Alex rides his bike to school. His speed changed form 0 m/s to 9 m/s in 10 seconds. What is his acceleration?

A. 9 m/s squaredB. 0.9 m/s squaredC. 15 m/s squaredD. 0.67 m/s squared

Key

1.b 2.b3.c4.b5.d6.c7.c8.a9.c10.b