Ch. 10 Forces.

Ch. 10

Forces

Forces

What is a force

• When you ride a bike, your foot pushes against the pedal. The push makes the wheels of the bike move.

• When you drop something, it is pulled to the ground by gravity.

What is a force

• Is a push or a pull. • a force is described by a push or a pull in

particular direction. • Forces are measured in Newton. • Named after Isaac Newton. • You exert one Newton of force when lifting a

lemon. • What SI unit measure forces?

Forces

• Can make objects move• Can make objects move faster• Can make objects move slower• Can make objects stop moving• Can make objects change direction• Can make objects change shape

Combining forces

• Often, more than a single force acts on an object at one time.

• A combination of forces on an object is called the net force.

• When forces that act in the same direction, the net force can be found by adding the strengths of the individual forces.

• When forces act in opposite directions, they also combine to produce a net force. (subtract)

Combining Forces

Unbalanced Forces

• Whenever there is a net force acting on an object, the forces are unbalanced.

• These forces can cause an object to start moving, stop moving, or change direction.

• Top is balanced• Bottom is unbalanced

Balanced Forces

• Equal forces are acting on one object in opposite directions are called balanced forces.

Answer the following Questions

Find the Net Force?

1. 2. 3. 4.

5 N 3 N

10 N 10 N

5 N 32 N 5 N

10N5N

Section 2 Friction and Gravity

• Friction is the force that two surfaces exert on each other when they rub together.

• The strength of the force of friction depends on two factors.

How hard they push together and they type of surfaces involved.

A smooth surface is much easier to slide on.

Friction

Gravity

• A force that pulls two objects towards each other.

• Two factors that affect gravity1.Mass- the more mass the greater the

gravitational pull. 2.Distance- the farther apart two objects are the

less gravitational pull.

Gravity

Section 3

Newton’s 1st law of motionor law of inertia

• An object at rest will remain at rest, and an object at a constant velocity will stay at a constant velocity unless acted on by an unbalanced force.

• Inertia is the tendency of an object to resist motion.

Newton’s 2nd law

• Acceleration depends on the object’s mass on the net force acting on the object.

• Acceleration=net force/ mass• Net force = mass X acceleration

Calculate

• A speedboat pulls a 55 kg water skier. The force causes the skier to accelerate at 2.0 meters per second per second. Calculate the net force that causes this acceleration.