 Today we are going to talk about Newton's three laws of motion and how they relate to vehicular accident investigations. Let's look at Newton's first law. The law states an object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This law is often called the law of inertia. In other words, objects tend to do what they're already doing. Inertia means that an object will always continue moving in its current speed and direction until some other force causes its speed or direction to change. This is why it's important to wear seatbelts in cars. When a car is moving and comes to a sudden stop, your body will want to continue to move in the original direction of the car. The same goes for objects that are not moving. An object will remain at rest until some force makes it move. So, there are two states of inertia, the state of rest and the state of moving. Sometimes it's hard to see inertia because of a force called friction. When two objects rub together, they create energy that causes a release of heat. You can feel this when you rub your hands together. What you're feeling right now is friction. Friction is a force that resists the movement of an object by acting in the opposite direction of the moving object. Think of the brakes you use to stop your car. If a car comes to a stop at a stop sign, it slows because of the friction between the brakes and the wheels. The friction stops the wheels from turning and counteracts the inertia moving the car forward. What happens if that same car tries to stop when it's raining? Friction is still there, but the liquid makes the road much smoother and decreases the friction. Less friction means it is harder to stop and easier for a car to slide out of control. That's why there are so many accidents in bad weather. Newton's second law states that acceleration is produced when a force acts on a mass. The greater the mass of the object being accelerated, the greater the amount of force needed to accelerate that object. This is expressed by the equation force equals mass times acceleration. For example, large cars have more mass than small cars, and it takes more force to make them accelerate and decelerate than it does for small cars. This is why large cars guzzle more gas. Newton's third law of motion states for every action there is an equal and opposite reaction. This means that for every force there is a reaction force that is equal in size, but opposite in direction. Whenever an object pushes another object, it gets to push back equally hard in the opposite direction. For example, when two cars experience a head-on collision, the cars will exert forces on each other, and they will be propelled away from each other after impact.