Forces Chapter 3

Force of Gravity Lab Does the speed of a falling object depend on the object’s mass? P. 67

Relationship of Force & Acceleration The greater the force, the greater the acceleration

The smaller the mass, the greater the acceleration

Newton’s Second Law The acceleration of an object is in the same direction as the net force, and the acceleration can be calculated from the following equation:

Force = mass x acceleration

Calculate the force need to move a 5kg box with an acceleration of 2 Calculate the force need to move a 5kg box with an acceleration of 2.5m/s2

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Calculate the force need to move a 3kg book with an acceleration of 4 Calculate the force need to move a 3kg book with an acceleration of 4.3 m/s2

Calculate the mass of an object that accelerates at a rate of 3 m/s2 when it is pushed with a force of 9 Newtons.

Calculate the acceleration of a 6 Calculate the acceleration of a 6.1 kg object is pulled with a force of 30.5N

Friction The force that opposes the sliding motion of two surfaces that are touching eahc other depends on 2 factors Kind of surfaces Force pressing between them

3 types of friction 1. Static friction: the force that prevents two surfaces from sliding past each other

2. Sliding friction: force that opposes the motion of two sliding past each other

3. Rolling friction: force between a rolling object and the surface it rolls on

Air Resistance Friction-like force that opposes the motion of objects that move through air Size, shape, speed, affect the amount of air resistance

Air Resistance (cont) Without air resistance, all falling objects would accelerate equally

Feathers Ball slow motion

Terminal Velocity The force of air resistance equals the force due to gravity Object’s fastest speed The object no longer accelerates and remains at the high constant velocity

Gravity An attractive force between any two objects It depends on the masses of the objects and the distance between them

Gravity The greater the mass, the greater the force

The earth’s mass is so great, that we can observe its force of gravity on us.

gravity

Comparing Friction! Object Height (cm) Type of Friction Observed

Weight- gravitational force on an object Weight= mass x acceleration due to gravity

Weightlessness Weightlessness exists when you are in free fall

Projectile Motion The path of an object(projectile) with the force of gravity Gravity adds the vertical motion

Observing Air Resistance

Centripetal Force Acceleration towards the center of a curved or circular path is centripetal acceleration The net force exerted toward the center of a curved path is centripetal force.

Newton’s 3rd Law of Motion Every action force has an equal and opposite reaction force

Momentum= mass x velocity The property of a moving object that is the product of its mass and velocity Related to how much force is need to change the object’s motion Momentum= mass x velocity

What is the momentum of a 7kg ball traveling at a velocity of 3.1 m/s? p = 7kg x 3.1 m/s P = 21.7 kg m/s

What is the mass of a truck that has a momentum of 43,200 kg m/s and a velocity of 24m/s?

p. 86 #1-3

Force and Changing Momentum   Force = Force = mass x acceleration Force = mass x velocity

Law of Conservation of Momentum Momentum within a system is transferred, not changed.