# Newton's Second Law of Motion

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### Newton’s Second Law of Motion :

1 Newton’s Second Law of Motion I can describe how Newton’s Laws of Motion apply to everyday situations. I can calculate the acceleration, mass or force of an object when using Newton’s 2nd law.

### Newton’s Second Law :

2 Newton’s Second Law Force = Mass x Acceleration Force is measured in Newtons ACCELERATION of GRAVITY(Earth) = 10 m/s2 Weight (force) = mass x gravity (Earth) 2

### Formulas to remember :

Formulas to remember Acceleration = change in velocity time What is the cause of acceleration? FORCE

### Force causes Acceleration :

Force causes Acceleration Example – hockey puck on ice Still until force is placed on it Stays moving in a straight path until another force causes it to accelerate Change direction Speed up Slow down Change in velocity  acceleration

### Acceleration :

5 Acceleration Acceleration is directly related to the size of the force and the direction of the force. It accelerates in the direction you push or pull it.

### Net force causes acceleration :

Net force causes acceleration Combination of force yields acceleration Double the force – double the acceleration

### In other words…. :

7 In other words…. Large Force = Large Acceleration F a

### In other words…. :

8 In other words…. Small Force = Small Acceleration F a So….if you push twice as hard, it accelerates twice as much.

### But there is a twist…. :

9 But there is a twist…. Acceleration is INVERSELY related to the mass of the object.

### In other words…..using the same amount of force…. :

10 In other words…..using the same amount of force…. Large Mass a Small acceleration Small Mass Large acceleration a

### Mass resists acceleration :

Mass resists acceleration Example Full shopping cart vs. empty shopping cart The greater the mass the more force it takes to accelerate the object Acceleration is inversely proportional to mass

### Using consistent units :

Using consistent units a = F m a =acceleration (m/sec2 ) F = force (newtons - N) m = mass (kg)

### Friction :

Friction Is a force Must be in contact Direction opposite to motion Force is needed to overcome friction Caused by irregular surface

### Extent of friction :

Extent of friction Depends on kinds of material How much surface are pressed together Examples Rubber on concrete Steel on steel Guard rails are now concrete instead of steel

### Friction in Fluids :

Friction in Fluids Liquid friction can be quite high Air resistance – notice at high speeds Biking or skiing

### Questions :

Questions Two forces act on a book resting on a table: its weight and the support force from the table. Does a force of friction act as well? No, not unless the book tends to slide. Friction only acts when there is motion

### Question :

Question Suppose a high-flying jet cruises with a constant velocity when the thrust from its engines is a constant 80,000 N. What is the acceleration of the jet? What is the force of air resistance acting on the jet?