1. Impulse A car got stuck in the snow and you were asked to help get the car free. Do you push with a lot of force for a short period of time, or do you push with the same amount of force but for a longer period of time? Pushing a stuck car for a long period of time will often get it free. An impulse is the change in momentum of an object. Impulse = Force x time J = Ft Thus, pushing the car for a longer period of time will create a larger change in momentum, making the car go forward. Ft = mv

2. How do you decrease the momentum an object has? Imagine you are driving a car that is out of control. You have two choices in stopping your car: Either slamming into a hard concrete wall or into a soft haystack. Which do you choose? In both cases, you want the momentum of the car to become zero (when it stops). Thus, both cases will have the same impulse (same change in momentum). According to the impulse equation, the shorter the time of contact, the greater the force on that object. Thus, slamming into a wall will cause you to stop really fast, but you will feel a larger force from the impact. Hitting the haystack will take a long time to stop, thus, lowering the amount of force that is felt.

3. Which impulse would produce a greater force? 1. When you are jumping down from a chair onto the floor, either landing with bent knees, or landing with stiff / straight legs. 2. Falling onto a mattress or falling onto a concrete floor. 3. When a person punches your face in boxing, either move into a punch or move away from a punch.

4. Which impulse would produce a greater force? 1. When you are jumping down from a chair onto the floor, either landing with bent knees, or landing with stiff / straight legs. 2. Falling onto a mattress or falling onto a concrete floor. 3. When a person punches your face in boxing, either move into a punch or move away from a punch. Answers: –1. Stiff / straight legs. –2. Concrete floor. –3. Move into a punch.