8.2 Impulse

8.2 Impulse

• Once the force is calculated, it can be used to find thevelocity just after impact and the change in time.

• Substitute the values for the initial and final velocities into the equation above to determine the change in momentum.

• The force that Venus Williams' racquet exerts on the tennis ball was not due to the racquet, but due to the force of gravity.
• This problem could be solved by first finding the acceleration and then using the strategy used in this example, but one additional step would be required compared with the strategy used in this example.

• The effect of a force on an object depends on a number of factors.
• The tennis racquet's force is larger than the gravity of the ball, so it would reverse the momentum of the ball if it were thrown upward.
• The change in momentum is what we are talking about.

• The change in momentum is the same as the change in impulse.

• The average net external force is equal to the change in momentum.

• The name impulse is given the quantity.

• There are many ways in which an understanding of impulse limbs can save lives.
• When there is a sudden stop, the net force on the occupants in the car can act over a longer time.
• If an air bag is not used, the force to bring the occupant to a stop will be less than if it is used.
• Cars today have plastic parts.
• The lighter weight of plastic results in better gas mileage.
• In the event of a head-on collision, a car will crumple.
• The force on the car will be less if the collision time is longer.

• If the force on the bones is too large, they will break.
• If you land stiff-legged on a hard surface, the force on your legs can be immense.
• Rolling on the ground after jumping from the table or landing with a parachute gives the force on you from the ground time to act.

• Two identical billiard balls strike a rigid wall with the same speed, and are reflected without any change of speed.
• The first ball hits the wall.
• The second ball strikes the wall at an angle of from the opposite side, and bounces off at an angle of from the opposite side.

• To determine the force on the wall, consider the force on the ball due to the wall usingNewton's second law and then apply his third law to determine the direction.
• To be positive in the initial direction of motion, you have to assume the - axis is normal to the wall.
• You can choose to be along the wall in the plane of the second ball's motion.
• The direction of the momentum is the same as the direction of the velocity.

• The first ball bounces into the wall and causes a force on it.
• The wall exerts force on the ball.
• The second ball has the same momentum component in the direction, but reverses its component as seen by sketching a diagram of the angles involved.

• The force of the wall on each ball is in the direction of the change in momentum for the balls.

• The change in momentum is the same for each ball as it is for the ball.

• The speed of each ball before and after hitting the wall is what we should be looking at.
• Take into account the change in the first ball's momentum when choosing the - axis and - axis.

• The change in momentum is called the impulse.
• The -component of impulse is the same as the -component of impulse.

• The second ball has a change in momentum.

• Changes do not sign after the collision.
• The -component of impulse is the same as the -component of impulse.