force

contact force

noncontact force

net force

unbalanced forces

balanced forces

Newton’s first law of motion

2.1 Combining Forces

Force• When more than one force acts on an object, the combined

effect is caused by the sum of all applied forces.

2.1 Combining Forces

• A push or a pull on an object is a force.

Contact and Noncontact Forces• A contact force is exerted only when two objects are

touching.

2.1 Combining Forces

• A noncontact force is exerted when two objects are not touching.

• Magnets exert a noncontact force on each other.

Force is a Vector

• Vectors have magnitude and direction.

• Force has a direction and a magnitude.

• Force is measured in Newtons.

2.1 Combining Forces

Combining Forces• When more than one force acts on an object, the

forces combine.

• The combination of all the forces acting on an object is called the net force.

2.1 Combining Forces

Combining Forces in the Same Direction

• Forces are vectors and require a reference direction.

• When forces in the same direction combine, the net force is in the same direction and the size of the force is the sum of the forces.

2.1 Combining Forces

Combining Forces in the Same Direction (cont.)

• If two people push the dresser to the right, the forces are added together.

2.1 Combining Forces

Combining Forces in Opposite Directions

• When forces in opposite directions combine, the net force is in the direction of the larger force.

• The size of the net force is the difference between the two forces.

2.1 Combining Forces

Combining Forces in Opposite Directions (cont.)

• Two people exerting a force in opposite directions show how vectors combine to create net force.

2.1 Combining Forces

Unbalanced and Balanced Forces• If the net force on an object is not zero, it is an

unbalanced force.

• If the net force on an object does equal zero, it is a balanced force.

2.1 Combining Forces

Balanced Forces

2.1 Combining Forces

Balanced Forces and Motion• If two people push with the same force, the

dresser does not move.

2.1 Combining Forces

• The forces have the same magnitude.

• The forces are in opposite directions.

• The net force on the dresser is zero and the forces are balanced.

• The motion of the dresser does not change.

Unbalanced Forces and Motion

• Unbalanced forces change motion.

• If two people push with different force, the dresser moves.

• The forces have a different magnitude and are in opposite directions.

• The net force on the dresser is not zero and the forces are unbalanced.

• The dresser moves in the direction of the larger force.

2.1 Combining Forces

Newton’s First Law of Motion• If the net force on an object is zero, the velocity of

the object does not change.

• If the net force is zero and the object is at rest, it remains at rest.

• If the net force is zero and the object is moving, it continues to move in a straight line with constant speed.

2.1 Combining Forces

Newton’s Laws of Motion

Inertia and Mass

• Mass is the amount of matter in an object.

• The more mass an object has, the more inertia it has and the harder it is to change its motion.

• A bicycle is easier to push than a car because it has less mass.

2.1 Combining Forces

Lesson 1 Review

Which of the following changes occur when an unbalanced force acts on an object?

A motion

B mass

C inertia

D weight

2.1 Combining Forces

Lesson 1 Review

What is the net force acting on a door if one person pushes to the right with a force of 2000 N and a second person pushes with a force of 1500 N to the right?

A 3500 N to the right

B 3500 N to the left

C 500 N to the left

D 500 N to the right

2.1 Combining Forces

Lesson 1 Review

You are riding a bike. In which of the following situations are the forces acting on the bike balanced?

A You pedal to speed up.

B You turn at constant speed.

C You coast to slow down.

D You pedal at constant speed.

2.1 Combining Forces

Balanced & Unbalanced Forces

• Balanced Skateboard Forces

• Draw the skateboard and the vectors in each direction to cause balanced forces.

• Unbalanced Frisbee Forces

• Draw the frisbee and the vectors in each direction to cause unbalanced forces.

• Unbalanced Skateboard Forces

• Draw the skateboard and the vectors in each direction to cause unbalanced forces.

• Balanced Frisbee Forces

• Draw the frisbee and the vectors in each direction to cause balanced forces.