Laws, friction, and Gravity

A force can cause a resting object to move, or it can accelerate an object by changing the objects speed or direction. We measure force in Newtons (N) 1N=1kg*m/s 2 Use an arrow to represent the direction and strength of force. FORCES

Forces can be combined by adding or subtracting. If two forces are working the same direction, these forces can be added together. ex: 5N+3N=8N Forces can be combined by adding or subtracting. If two forces are working the same direction, these forces can be added together. ex: 5N+3N=8N COMBINING FORCES

If two forces are working opposite of each other, these forces can be subtracted from each other for a combined force. We call these combined forces the NET FORCE. COMBINED FORCES

A truck is being pulled by a force of 5N and another force is added in the same direction of 10N. What is the total net force being applied to the truck? A tug of war game has erupted between two teams. Team A is pulling with a force of 4N and Team B is pulling with a force of 6N. What is the net force of the game? PRACTICE ON COMBINED FORCES

Balanced forces: When forces on an object are balanced, net force is zero and there is no change in motion. Ex: BALANCED FORCES

Unbalanced Forces: When an unbalanced force acts on an object, the object accelerates. Ex: UNBALANCED FORCES

shows/videos/assignment-discovery-shorts-newtons-laws-of- motion.htm shows/videos/assignment-discovery-shorts-newtons-laws-of- motion.htm Law 1: Law of inertia…an object in motion will stay in motion unless another force is acted upon it. Law 2: The acceleration of an object is equal to the net force actin on it divided by the objects mass. Law 3: Every action has an equal and opposite reaction. NEWTON’S LAWS OF MOTION

An object in motion will stay in motion. An object at rest will stay at rest. Objects all have the potential to move but do not do so unless a force is acted upon them. This is called inertia. Momentum is an example of how this is true. LAW 1

An object at rest will have a momentum of zero. If there were no forces then the momentum of an object would be constant. BUT there is always another force. Momentum=Product of an objects mass and its velocity An object with a large momentum is hard to stop. Momentum is represented by p=mv Momentum at rest =zero. Ex: A bowling ball has a velocity of 5m/s and a mass of 6kg. What is the momentum. MOMENTUM

Ex: a rolling chair has a velocity of 3m/s and a mass of 4 kg. What is the momentum? Do you think that that a really heavy object moving slow could have the same momentum as a really light object moving fast? MOMENTUM CONTINUED

If no net force acts on a system, then the total momentum does not change. If one object loses momentum then the other object gains momentum. This can happen in a couple different ways Look at the diagram on the next page. CONSERVATION OF MOMENTUM

Friction-a force that opposes the motion of objects that touch as they move past each other. Four Main Types of Friction: 1.Static Friction 2.Sliding Friction 3.Rolling Friction 4.Fluid Friction FRICTION

The frictional force that acts on objects that are not moving The direction opposite of an applied force. Ex: Every time you step you push off the ground. The static friction between your foot and the ground keep you from sliding. Ex: STATIC FRICTION

Opposes the direction of motion of an object as it slides over the floor. Sliding Friction < Static Friction It takes less force to keep an object moving than to make it move from a stopped position. Ex: SLIDING FRICTION

Acts on a rolling object. Rolling friction<Sliding friction Ex: Ball bearing-a set of small round balls set between two smooth surfaces. Where do they use ball joints and why would they use these? ROLLING FRICTION

Opposing motion through a fluid Fluid friction increases as the speed of the object moving through it increases. Ex: Stirring cake batter. The faster you stir the batter, the greater the friction and the harder it is to stir. Fluid Friction through the air is called air resistance. Ex: reason why skaters use slick suits to cut down on the air resistance. FLUID FRICTION

A force that acts between two masses. Gravity has the constant acceleration of 9.8m/s 2 If the rate of gravity is at 9.8m/s 2 then what do you think the speed of an object in free fall is? GRAVITY

Gravity causes objects to accelerate downward, whereas air resistance acts in the direction opposite to the motion and reduces the acecleration. When these forces are balanced, (meaning the force of air resistance and the force of gravity equal each other) the objects acceleration is zero and velocity continues at a constant rate. This is called TERMINAL VELOCITY. FALLING OBJECTS

Law 2: The acceleration of an object is equal to the net force actin on it divided by the objects mass. F=MA Force is equal to the mass of an object multiplied by its acceleration. Practice problem work sheet! NEWTON’S 2 ND LAW OF MOTION

Law 2: The acceleration of an object is equal to the net force actin on it divided by the objects mass.(force equals mass X acceleration) F=MA Weight is the force of gravity acting on an object Weight= mass X acceleration due to gravity. Mass is a measure of the inertia of an object; weight is the force of gravity acting on an object. WEIGHT AND MASS

Newton's third law of motion: For every action there is an equal and opposite reaction. What this means is that whenever a force is acted upon an object, there is an equal force that also takes place. Ex: Hammer and a nail A swimmer in water. Why do these forces not cancel each other out? ACTION AND REACTION FORCES